Improves the README section about query permissions:
- Removes http/https from the examples; we don't actually expect people
  to query for http(s) support in general (since generally a browser can
  assumed to be available), so it's an odd thing to show.
- Updates the comments in the Android example to clarify that it's about
  querying for support, not launching.
- Makes the iOS and Android sections have parallel structure so they are
  easier to read.

Fixes flutter/flutter#102630