Merge pull request #192 from Susurrus/readme

Updated the readme with some more Visual Studio reqs.

README

@@ -82,7 +82,7 @@ Windows XP/7:
 
 1) Download and install the Qt libraries for Windows from https://qt.nokia.com/downloads/ (the Visual Studio 2008 or 2010 version as appropriate)
 
-2) Download and install Visual Studio 2008 or 2010 Express Edition (free) from https://www.microsoft.com/visualstudio
+2) Download and install Visual Studio 2008 or 2010 Express Edition (free) from https://www.microsoft.com/visualstudio. If using Visual Studio 2010, make sure you are running at least SP1. There is a linking error you'll encounter otherwise that will prevent compilation.
 
 3) Go to the QGroundControl folder and then to thirdParty/libxbee and build it following the instructions in win32.README