[docs] Updating Flipper instructions - still blocked by idb issues upstream

Summary:
**For Apple silicon, this edit is blocked by idb issues https://linear.app/comm/issue/ENG-226/[docs]-idb-failed-to-install**

Added instructions to Flipper section for specifying Android SDK.
Had to move Flipper section under Android Studio section to ac[comm]odate this, as the Android SDK location is found easily via Android Studio settings.

I updated Flipper to v0.122.0, and noticed that "File" is missing from the preferences. Therefore, I removed the suggestion to access Flipper settings via File, as it's no longer available.
The alternative way to access Settings is just to click the Cog in bottom left corner, but I don't like it. Couldn't find a shortcut.

Also told users to enable "React Native keyboard shortcuts".

Test Plan: Re-installed Flipper to see if the instructions I added worked.

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

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

Differential Revision: https://phabricator.ashoat.com/D2480