Updated "Getting Started".

Removed OSX/Linux instructions for now as they were out of date and
didn't say much anyway.

docs/tutorial/gettingstarted.md

@@ -6,10 +6,5 @@
 
 The easiest way to try out Avalonia is to install the Visual Studio Extension.
 
-This will add a Avalonia project template and a Window template to the standard Visual Studo “Add” dialog (yes, icons still to come :) ):
-
-## OSX / Linux
-
-It is a little more manual on non-Windows platforms, but using Xamarin Studio you can install the Avalonia NuGet package.
-
-![](images/add-packages.png)
+This will add a Avalonia project template and a Window template to the standard Visual Studo “Add”
+dialog (yes, icons still to come :) ):