website/docs: Add warning for timezone mounts (#3022)

Improve documentation: #3005

website/docs/installation/docker-compose.md

@@ -93,6 +93,15 @@ To start the initial setup, navigate to `https://<your server>/if/flow/initial-s
 
 ## Explanation
 
+:::warning
+The server assumes to have local timezone as UTC.
+All internals are handled in UTC, whenever a time is displayed to the user in UI it gets localized.
+Do not update or mount `/etc/timezone` or `/etc/localtime` in the authentik containers.
+This will not give any advantages.
+On the contrary, it will cause problems with OAuth and SAML authentication,
+e.g. [see this GitHub issue](https://github.com/goauthentik/authentik/issues/3005).
+:::
+
 The docker-compose project contains the following containers:
 
 -   server