Document how to manage plugins and extensions (#6909)

* Add docs for plugins

* fix some wording

docs/source/configuration.md

@@ -4,7 +4,8 @@
 :caption: Configuration
 :maxdepth: 1
 
-config_overview
+configuring/config_overview
+configuring/plugins
 Security <https://jupyter-server.readthedocs.io/en/stable/operators/security.html>
 extending/index.rst
 ```

docs/source/configuring/plugins.md

@@ -0,0 +1,21 @@
+# Managing plugins
+
+Notebook 7 uses the same extension system as JupyterLab. An extension can provide multiple plugins.
+
+```{note}
+See the [JupyterLab documentation](https://jupyterlab.readthedocs.io/en/latest/user/extensions.html) to learn more about the extension system.
+```
+
+## Examples
+
+### Disabling the download button
+
+By default Notebook 7 provides a way to download files from the file browser. This functionality consists of a context menu entry and a main menu entry. They are provided by an application plugin that can be disabled.
+
+To disable the download entry of file browser context menus, open a terminal and run the following command:
+
+```text
+jupyter labextension disable @jupyterlab/filebrowser-extension:download
+```
+
+Then restart the application and refresh the page.