Fix link to diagnostic screen setup
Fix link to diagnostic screen setup

Summary: Was pointed out to be broken in https://github.com/facebook/flipper/issues/1254

Reviewed By: mweststrate

Differential Revision: D22117270

fbshipit-source-id: 15947f9e0373b4324165de7d1a2a6be70a8e652c

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