Update @MountSpec docs to be more informative
Update @MountSpec docs to be more informative

Summary: See title

Reviewed By: muraziz

Differential Revision: D7934165

fbshipit-source-id: 43d8ce8c6add323f1c6769ff2912f4898f6bee6f

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