Added info from commons-app/apps-android-commons#4474

Author: nicolas-raoul

docs.html

@@ -73,6 +73,16 @@ <h2 id="nearby-query"><a href="#nearby-query">Customizing the Nearby query</a></
         <p>The names of the outputs can not be changed.</p>
         <p>Variable names are replaced by the app before executing the query.</p>
 
+        <h2 id="app-versions"><a href="#app-versions">App versions</a></h2>
+        <p>To know what version of the app you are using, open the "About" dialog and check the string immediately below the "Commons" title.</p>
+        <p>This string also tells you what channel you are using:</p>
+        <ol>
+            <li>Stable if the version string contains one dot. Example: 3.0</li>
+            <li>Beta if the version string contains two dots. Example: 3.0.1</li>
+            <li>Alpha if the version string contains three dots. Example: 3.0.1.1019</li>
+        </ol>
+        <p>If you want to switch back to a previous version, please <a href="https://github.com/commons-app/apps-android-commons/releases">download the APK of the version you want</a> and install it (you may need to uninstall first).</p>
+
         <h2 id="getting-app-logs-from-android-studio"><a href="#getting-app-logs-from-android-studio">Getting app logs from Android Studio</a></h2>
         <p>Brief walkthrough for users on how to post logs if they are encountering issues.</p>
         <ol>