Wiki: Update Android installation docs

[marcustyphoon]

File

https://github.com/AprilSylph/XKit-Rewritten/wiki/Installation

Details

XKit Rewritten can now be installed on Firefox for Android without special instructions.

[marcustyphoon]

Could also be mentioned in readme.md.

[marcustyphoon]

https://github.com/AprilSylph/XKit-Rewritten/wiki/Installation/_compare/ed64ec16f843ca0bcc7d03d845be0aea563af679

Sighs, this "just edit it and discuss elsewhere if desired" workflow feels terrible. Anyway, @AprilSylph I adjusted the wiki documentation here.

Not sure if we need to keep around the previous documentation or if we should mention the minimum version to be able to install directly off AMO; I also don't actually know what that minimum version is. The release notes seem to imply that it's 121, but a lot of the language around the change doesn't specify a version and sort of implies to me that it may work in older versions?