docs: add Mavenrepository configuration for Expo builds

[Nicklas-17]

This PR adds documentation for a crucial Maven configuration step when using Notifee with Expo projects.

Problem:
Many Expo users encounter the error "Could not find any matches for app.notifee:core" during Android builds. This happens because the Android build system cannot locate Notifee's native dependencies through Maven.

Solution:
Added documentation explaining how to configure extraMavenRepos in the expo-build-properties plugin to properly point to Notifee's native libraries. This configuration ensures the Android build system can find and resolve Notifee's core dependencies.

The added section:

• Explains the common error users might encounter
• Provides the exact configuration needed in app.config.js/app.json
• Places this information in a logical location within the Expo setup instructions

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Hello 👋, this PR has been opened for more than 2 months with no activity on it.

If you think this is a mistake please comment and ping a maintainer to get this merged ASAP! Thanks for contributing!

You have 15 days until this gets closed automatically