Document editing AndroidManifest.xml

In the AndroidManifest.xml there is a bit of undocumented magic at the moment, and when you generate a manifest in Qt Creator, you'll get all this magic with no explanation. This can in part be fixed by adding comments in the manifest, but I think it should also have a place in documentation.

An example is removing default permissions/features from your application: By default, your app will get permissions and features based on the modules you access. This is convenient, because it means you can develop without experiencing crashes.

However, before you go into productions, it is recommended that you edit the manifest and replace the place-holders for the default ones with your own permissions based on what your application actually does.