Better documentation for how to avoid checking in BAML client files

[anerli]

Best practice is to have BAML src files be source of truth and checked and generated client files should be in gitignore. Docs could benefit from laying out specific recommended ways to do this and when to generate the client in this kind of setup.

Discord thread: https://discord.com/channels/1119368998161752075/1352291250400792727

[linear[bot]]

BAML-272 Better documentation for how to avoid checking in BAML client files