headscale: Android configuration

1. Install the official Tailscale Android client from the Play store
2. Open the Tailscale app
3. Tap the top-right options menu button and select "Accounts".
4. Tap the top-right options menu button and select "Use an alternate server".
5. Enter the custom server URL: https://users.nynex.de
6. Enter your credentials and log in. The client should now be connected to our server