Community TFS Build Manager is really useful add-on to VS 2010/2012/2013 to create Build/Release Notes automatically.
You can download this free from Visual Studio Gallery and this project source code can be found here at codeplex if you want to further customize.
Once you install Community TFS Build Manager you can see a new link appear in VS Team Explorer as below.
Launch this tool and select the builds.
Right click on the build which you want to generate a release note, and click on "Experimental Build Note".
Set the necessary information.
Click "Generate" and there you go...
Awesome. Isn't it?
For information on getting the necessary changesets associated to a build see my post TFS 2012 - Get a Release Build With Changesets Associated From a Given Changeset