fix: revert README.md to v1 documentation

Commits 2182205, 4fc49c6, and 1a8c14a accidentally updated README.md
with v2 content after it was intentionally reverted to v1 docs in 2137c8f.

Restore README.md to the v1 state. All three commits already applied their
changes to README.v2.md as well, so no content is lost.

Author: maxisbey