[docs] Fixing some nits I found in the "Running mobile app on iOS/Android" sections

Summary:
While going through the iOS physical device instructions, I found some naming conventions to be addressed in the "iOS Simulator" section. Adding comments with links to the naming conventions.

Sorry if this diff does a few things, I found some inconsistency in the "Android Emulator" section to be addressed as well. These were all really small changes, and I felt they'd be ok in this one diff.

Test Plan: Looked at the official docs. Will provide links.

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: benschac, ashoat, palys-swm, Adrian, karol-bisztyga, boristopalov

Differential Revision: https://phabricator.ashoat.com/D2706