Added StackOverflow reference to the Forums section

While I was aware of the StackOverflow Q&A site all these years, my preference has been always the specific MSDN Visual Studio Integrate forum (formerly MSDN Visual Studio Extensibility forum), and I have only answered a couple of questions in StackOverflow, mainly pointed by someone by e-mail.

However, today I have registered in StackOverflow, added my favorited tags (vsx, vs-extensibility, vsix, vspackage, visual-studio-addins, envdte, visual-studio-sdk, etc.) and I hope to get used to that site and visit it as often as I do with the MSDN VSX forum.

I have also added it to the Forums section of this VSX site since I find it a valuable resource to get answers: http://www.visualstudioextensibility.com/forums/