README updates for missing and deprecated Android documentation

[esalaza]

Changes

Update the README for:

• 21 (content by @DiogoParrinha)

• 41

Thank you :)

[jcesarmobile]

Thanks for the PR, but I've updated the plugin so users don't have to add the permissions/queries manually, so this changes are no longer needed. I've also removed the registering part for android since that's no longer possible on Capacitor 4