update README file (#1144)

* update README file

update VS 2010 as the minimal version of required Visual Studio

* Rephrase the MS VS requirement

Rephrase the VS version sentence
diff --git a/README.md b/README.md
index 5ffd2ae..75639e9 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 -   yotta
 -   GNU Make
 -   CMake
--   Microsoft Visual Studio (Visual Studio 6 and Visual Studio 2010)
+-   Microsoft Visual Studio (Microsoft Visual Studio 2010 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.