Add an accessibility development guide

[xuelgong]

As requested by the FB team @rachelnabors , we'd like to share some thoughts for making accessible react native components to enrich the react native accessibility documentation.

[react-native-bot]

Deploy preview for react-native ready!

Built with commit 4a4c13b159f70cc0226c6cb80e2f560190a969b8

https://deploy-preview-2219--react-native.netlify.app

Changes to docs/ are reflected in the next "master" version.

Thank you for your contributions.

_{How to Contribute • Documentation Sources}

[nearestnabors]

Thanks so much for your contribution! The queue is a little backed up at the moment, but I Will review this as soon as possible :)