Add troubleshooting step for provider authentication (#411)

Added troubleshooting step for music provider authentication issues.

Author: OzGav

docs/faq/troubleshooting.md

@@ -27,6 +27,8 @@ Ensure local files are [tagged properly](https://music-assistant.io/music-provid
 
 If it is a playback issue then turn on QUEUE FLOW MODE in the settings for the specific player (where that is available).
 
+If it is a music provider issue and the provider requires authentication then clear the authentication and re-login.
+
 If it is a frontend issue or related to logging in to a provider which requires redirection to another website then try a different browser. If you are trying on a mobile device then try on a laptop or PC. Firefox and Safari are known to have deficiencies.
 
 Review the applicable player or music provider documentation to see if there are known issues or specific troubleshooting steps or fixes.