Docs on how to include fb-only parts into open-sourced plugins
Docs on how to include fb-only parts into open-sourced plugins

Summary: Added docs on how to include fb-only parts into open-sourced plugins

Reviewed By: mweststrate

Differential Revision: D27678276

fbshipit-source-id: e0c3de8ed57a7d25f291e8e6ac15ed32812a0cbc

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper