Update documentation for contrib (#12424)

* Update __init__.py

Remove ## for standardization of api docs

* Create README.md

Add README to define this directory's purpose

* Update __init.py

Markdown styling does not show up well in api docs

* Update README.md

Add short mention of describing what to deprecate

* Update README.md

Capitalize title

* Update README.md

Revert README change

* Delete README.md