Custom layout docs (#476)
Custom layout docs (#476)

Summary:
Add documentation about OnShouldCreateLayoutWithNewSizeSpec
Pull Request resolved: https://github.com/facebook/litho/pull/476

Reviewed By: muraziz

Differential Revision: D13622714

Pulled By: adityasharat

fbshipit-source-id: c29cd12a4a2e9fd24a6d8c0975689f75b9802f0e

facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho