DOCS: Describe SAF protocol for Android

[sev-]

Described the new SAF workflow for Android. Thanks to @lephilousophe for the screenshots.

[antoniou79]

I've added a couple of comments to change the example parent folder's name from "myGames" to "ScummVMgames" to match the screenshots.

Also, in the same page (android.rst) there is a "Note" in the "What you'll need" section that reads ".. note::

ScummVM has been tested to work up to Android 10. Currently there are some file browsing limitations with Android 11. The ScummVM team are working to resolve these."

This can be removed or reduced to:
".. note::

ScummVM has been tested to work up to Android 12."

And also there is a "Known issues" section in the bottom where the first bullet can be removed.
This bullet reads:
"- On some newer devices, there is an issue if the saved path is outside the app's internal (or external) storage. The ScummVM team is currently working on a fix."
It can be removed.

[sev-]

@antoniou79 I addressed the issues. Please review.

[lephilousophe]

Looks good to me.
It's really centred around migration from an old version and not for newcomers but maybe the UI is simple enough to not need dedicated instructions.