Updated c_sharp_basics.rst

Added some extra information about setting up C# for Godot in Windows.

getting_started/scripting/c_sharp/c_sharp_basics.rst

@@ -45,6 +45,7 @@ C# in Godot. If you don't plan on using the Visual Studio IDE,
 you can download just the
 `Visual Studio Build Tools <https://visualstudio.microsoft.com/thank-you-downloading-visual-studio/?sku=BuildTools&rel=15>`_
 instead.
+Make sure you at least have the .NET Framework 4.5 targeting pack installed, you can get it using any of the installers mentioned above inside the "Individual components" tab.
 
 macOS and Linux
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