Add a simple contributing file to help onboard new users

CONTRIBUTING.md

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+# Contributing to Discovery Agent
+
+Thank you for your interest in contributing! This document provides guidelines and instructions for contributing.
+
+Note that this repository holds two separate components:
+
+- disco-agent: For CyberArk DisCo
+- venafi-kubernetes-agent: For TLSPK / Certificate Manager SaaS
+
+## Table of Contents
+
+- [Getting Started](#getting-started)
+- [Development Environment](#development-environment)
+- [Making Changes](#making-changes)
+- [Testing](#testing)
+- [Submitting a Pull Request](#submitting-a-pull-request)
+- [Code Review Process](#code-review-process)
+- [Additional Resources](#additional-resources)
+
+### Prerequisites
+
+Before you begin, ensure you have the following installed:
+
+- [Go](https://golang.org/doc/install) (version specified in `go.mod`)
+- [Make](https://www.gnu.org/software/make/)
+- [Git](https://git-scm.com/)
+- [Docker](https://docs.docker.com/get-docker/) (for building container images)
+
+To check which Go version will be used:
+
+```bash
+make which-go
+```
+
+It's also possible to use a vendored version of Go, via `make vendor-go`.
+
+### Repository Tooling
+
+Most of the setup logic for provisioning tooling and for handling builds and testing
+is defined in Makefile logic.
+
+Specifically, `the make/_shared` directory contains shared Makefile logic derived from
+the cert-manager [makefile-modules](https://github.com/cert-manager/makefile-modules/) project.
+
+### Setting Up Your Development Environment
+
+1. **Fork the repository** on GitHub
+
+2. **Clone your fork:**
+
+   ```bash
+   git clone git@github.com:YOUR-USERNAME/jetstack-secure.git
+   cd jetstack-secure
+   ```
+
+3. **Add the upstream remote:**
+
+   ```bash
+   git remote add upstream git@github.com:jetstack/jetstack-secure.git
+   ```
+
+4. **Run initial verification:**
+
+   ```bash
+   make verify
+   ```
+
+   This ensures your environment is set up correctly.
+
+## Development Environment
+
+### Local Execution
+
+To build and run the agent locally:
+
+```bash
+go run main.go agent --agent-config-file ./path/to/agent/config/file.yaml -p 0h1m0s
+```
+
+Example configuration files are available:
+- [agent.yaml](./agent.yaml)
+- [examples/one-shot-secret.yaml](./examples/one-shot-secret.yaml)
+- [examples/cert-manager-agent.yaml](./examples/cert-manager-agent.yaml)
+
+You can also run a local echo server to monitor agent requests:
+
+```bash
+go run main.go echo
+```
+
+### Useful Make Targets
+
+- `make help` - Show all available make targets
+- `make verify` - Run all verification checks (linting, formatting, etc.)
+- `make test-unit` - Run unit tests
+- `make test-helm` - Run Helm chart tests
+- `make generate` - Generate code, documentation, and other artifacts
+- `make oci-build-preflight` - Build container image
+- `make clean` - Clean all temporary files
+
+## Making Changes
+
+### Creating a Branch
+
+Always create a new branch for your changes:
+
+```bash
+git checkout -b feature/your-feature-name
+```
+
+Use descriptive branch names:
+- `feature/` for new features
+- `fix/` for bug fixes
+- `docs/` for documentation changes
+- `refactor/` for refactoring
+
+### Code Style
+
+This project follows standard Go conventions:
+
+- Run `make verify-golangci-lint` to check your code
+- Run `make fix-golangci-lint` to automatically fix some issues
+- Ensure all code is formatted with `gofmt`
+- Follow the [Effective Go](https://golang.org/doc/effective_go) guidelines
+- Most of the conventions are enforced by linters, and violations will prevent code being merged
+
+### Committing Changes
+
+1. **Stage your changes:**
+
+   ```bash
+   git add .
+   ```
+
+2. **Run verification before committing:**
+
+   ```bash
+   make verify
+   ```
+
+3. **Commit with a descriptive message:**
+
+   ```bash
+   git commit -m "Brief description of your changes"
+   ```
+
+   Write clear commit messages:
+   - Use the imperative mood ("Add feature" not "Added feature")
+   - Keep the first line under 72 characters
+   - Add additional context in the body if needed
+
+## Testing
+
+### Running Tests Locally
+
+Before submitting a PR, ensure all tests pass:
+
+```bash
+# Run unit tests
+make test-unit
+
+# Run Helm tests
+make test-helm
+
+# Run all verification checks
+make verify
+```
+
+### End-to-End Tests
+
+E2E tests run automatically in CI when you add specific labels to your PR:
+
+- Add the `test-e2e` label to trigger GKE-based E2E tests
+- Add the `keep-e2e-cluster` label if you need to keep the cluster for debugging (remember to delete it manually afterward to avoid costs)
+
+The E2E test script is located at [hack/e2e/test.sh](./hack/e2e/test.sh).
+
+### Writing Tests
+
+- Add unit tests for all new functionality
+- Place tests in `*_test.go` files alongside the code they test
+- Use the [testify](https://github.com/stretchr/testify) library for assertions
+- Aim for meaningful test coverage, not just high percentages
+
+## Submitting a Pull Request
+
+1. **Push your branch to your fork:**
+
+   ```bash
+   git push origin feature/your-feature-name
+   ```
+
+2. **Create a Pull Request** on GitHub from your fork to the `master` branch of `jetstack/jetstack-secure`
+
+3. **Fill out the PR description** with:
+   - Clear description of the changes
+   - Related issue numbers (if applicable)
+   - Testing instructions
+   - Any breaking changes or special considerations
+
+4. **Ensure CI passes:**
+   - All tests must pass
+   - Code must pass verification / linting checks
+   - No merge conflicts
+
+## Code Review Process
+
+### For All Contributors
+
+- PRs require approval before merging
+- Keep PRs focused and reasonably sized
+- Update your branch if `master` has moved forward:
+
+  ```bash
+  git fetch upstream
+  git rebase upstream/master
+  git push --force-with-lease origin feature/your-feature-name
+  ```
+
+### For CyberArk Contributors
+
+**Contributors from inside CyberArk should reach out to the cert-manager team for reviews for PRs which are passing CI.**
+
+The cert-manager team maintains this project and will provide code reviews and guidance for merging changes.
+
+## Additional Resources
+
+- [Project Documentation](https://docs.cyberark.com/mis-saas/vaas/k8s-components/c-tlspk-agent-overview/)
+- [Issue Tracker](https://github.com/jetstack/jetstack-secure/issues)
+- [Release Process](./RELEASE.md)
+- [cert-manager Community](https://cert-manager.io/docs/contributing/)
+
+## Getting Help
+
+If you need help or have questions:
+
+1. Check existing [issues](https://github.com/jetstack/jetstack-secure/issues) and [documentation](https://docs.cyberark.com/mis-saas/vaas/k8s-components/c-tlspk-agent-overview/)
+2. Open a new issue with the `question` label
+3. For CyberArk contributors, reach out to the cert-manager team
+
+## License
+
+By contributing, you agree that your contributions will be licensed under the license in the LICENSE file in the root directory of this repository.