Fix 2 instances of a typo in the desktop-lite NOTES and README (#640)

* Amend 'is installed is' to 'installed is'.

* Undo typo fix from README
Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

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Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

src/desktop-lite/NOTES.md

@@ -25,7 +25,7 @@ You can also connect to the desktop using a [VNC viewer](https://www.realvnc.com
 
 ## Customizing Fluxbox
 
-The window manager is installed is [Fluxbox](http://fluxbox.org/). **Right-click** to see the application menu. In addition, any UI-based commands you execute inside the dev container will automatically appear on the desktop.
+The window manager installed is [Fluxbox](http://fluxbox.org/). **Right-click** to see the application menu. In addition, any UI-based commands you execute inside the dev container will automatically appear on the desktop.
 
 You can customize the desktop using Fluxbox configuration files. The configuration files are located in the `.fluxbox` folder of the home directory of the user you using to connect to the dev container (`$HOME/.fluxbox`).