noted demo.cs deletion with link to history

Example/README.md

@@ -4,4 +4,6 @@ This example shows how to use the Terminal.Gui library to create a simple GUI ap
 
 This is the same code found in the Terminal.Gui README.md file.
 
-See [README.md](https://github.com/gui-cs/Terminal.Gui) for a list of all Terminal.Gui samples.
+See [README.md](https://github.com/gui-cs/Terminal.Gui) for a list of all Terminal.Gui samples.
+
+Note, the old `demo.cs` example has been deleted because it was not a very good example. It can still be found in the [git history](https://github.com/gui-cs/Terminal.Gui/tree/v1.8.2).