Migrate Compose API guidelines to markdown
Migrate Compose API guidelines to markdown

and check them into the repository for reference and contributions.

Test: n/a/
Change-Id: I8bb3017feb89bf41eb785dad343f06400210d9b0

AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx