feat: mention PyPI install mechanism

[henryiii]

See #27 (comment).

[pocc]

A longform explanation like cppcheck would be more helpful, because the clang-format already has packages available for every platform, i.e. something like

clang-format can also be installed with pip and tied to a version like so crazy cool commands using this repo. This can be useful when running CI runners to use a specific version.

I'm unclear (outside of this PR) how your repo enforces a version, and your README does not detail how? Could you provide an example?

[pocc]

I've gone ahead and added verbiage to point people to using pipx install clang-format. Please let me know if this language could be improved.