Add a clarifying comment for the download plugin. (#10092)

This expands on the changes in #10066, where the download entries are separated into a separate plugin that can be disabled. There have been a fair number of requests to disable downloading, which is impossible to do without server changes. This commit adds a comment clarifying that disabling this new plugin is more of a UX change rather than a functional change.

For more conversation around this, see #5274.

packages/filebrowser-extension/src/index.ts

@@ -300,7 +300,11 @@ const factory: JupyterFrontEndPlugin<IFileBrowserFactory> = {
 };
 
 /**
- * A plugin providing download + copy download link commands in the context menu
+ * A plugin providing download + copy download link commands in the context menu.
+ *
+ * Disabling this plugin will NOT disable downloading files from the server.
+ * Users will still be able to retrieve files from the file download URLs the
+ * server provides.
  */
 const downloadPlugin: JupyterFrontEndPlugin<void> = {
   id: '@jupyterlab/filebrowser-extension:download',