Update the VS version in the Readme file

Update the VS version in the README file to 2012, as this is the
minimal version supported.
diff --git a/README.md b/README.md
index 43065b1..add87d2 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@
 
 -   GNU Make
 -   CMake
--   Microsoft Visual Studio (Microsoft Visual Studio 2010 or later)
+-   Microsoft Visual Studio (Microsoft Visual Studio 2012 or later)
 
 The main systems used for development are CMake and GNU Make. Those systems are always complete and up-to-date. The others should reflect all changes present in the CMake and Make build system, although features may not be ported there automatically.
 
@@ -154,7 +154,7 @@
 
 ### Microsoft Visual Studio
 
-The build files for Microsoft Visual Studio are generated for Visual Studio 2010.
+The build files for Microsoft Visual Studio are generated for Visual Studio 2012.
 
 The solution file `mbedTLS.sln` contains all the basic projects needed to build the library and all the programs. The files in tests are not generated and compiled, as these need Python and perl environments as well. However, the selftest program in `programs/test/` is still available.