Add note about xmlns:android attribute for config.xml

[signalpoint]

PR Type

What kind of change does this PR introduce?

• [x] Documentation changes

New features/enhancements:

• [x] Documentation has been added / updated

What is the purpose of this PR?

Clarify documentation around config-file and push notification permissions.

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No