Add Android S3 docs in "Cloud Management"

[s-h-a-d-o-w]

Personally, I had no clue what you mean by "endpoint", tried S3 URLs first (particularly because I got to the form via "add existing vault" - I thought you might mean the vault URL) and only after a few trial & error attempts, I figured out that you mean s3.<region>.amazonaws.com (at least in case of not using a reseller).

Which is why I think it would be important to add. And I would be happy to work on it.

[SailReal]

Would be really cool, just add another entry to https://docs.cryptomator.org/en/latest/android/cloud-management/ which is technically https://github.com/cryptomator/docs/blob/main/source/android/cloud-management.rst .

...please also mention that the app currently requires the "Allow List All Bucket Names" scope (cryptomator/android#339).