Added Applications plugin readme

plugins/applications/README.md

@@ -0,0 +1,13 @@
+# Applications
+
+## Desktop Actions
+
+To enable desktop actions support, set `desktop_actions` in the applications plugin config
+file to `true` like so:
+
+`<anyrun config directory>/applications.ron`:
+```ron
+Config(
+  desktop_actions: true,
+)
+```