📝 Fix url to unity-launcher and tiny correction (#12084)

docs/api/shell.md

@@ -36,7 +36,7 @@ Open the given file in the desktop's default manner.
 
 ### `shell.openExternal(url[, options, callback])`
 
-* `url` String - max 2081 characters on windows, or the function returns false.
+* `url` String - Max 2081 characters on windows, or the function returns false.
 * `options` Object (optional) _macOS_
   * `activate` Boolean - `true` to bring the opened application to the
     foreground. The default is `true`.

docs/tutorial/desktop-environment-integration.md

@@ -22,7 +22,7 @@ See the [Progress Bar documentation](progress-bar.md).
 
 ## Unity Launcher
 
-See the [Unity Launcher documentation](unity-launcher.md).
+See the [Unity Launcher documentation][unity-launcher].
 
 ## Represented File for macOS Window
 
@@ -31,3 +31,5 @@ See the [Represented File documentation](represented-file.md).
 ## Dragging files out of the window
 
 See the [Native File Drag & Drop documentation](native-file-drag-drop.md).
+
+[unity-launcher]: https://help.ubuntu.com/community/UnityLaunchersAndDesktopFiles#Adding_shortcuts_to_a_launcher