Overhaul end user documentation

docs/user_documentation/plugins/index.md

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+# User plugins
+
+```{note}
+Your {term}`pod's <Pod>` admin needs to enable plugins for you to use them. If you can't find the plugins mentioned here, contact your pod admin.
+```
+
+Use plugins to extend Funkwhale's features. The Funkwhale collective maintains core plugins to make your listening experience even better. Developers can create extra plugins to add features to a pod.
+
+```{toctree}
+---
+maxdepth: 1
+caption: Core plugins
+---
+
+scrobbler_plugin
+listenbrainz_plugin
+maloja_plugin
+
+```