some minor text changes

Author: glennc

README.md

@@ -14,7 +14,7 @@ In order to be able to get new builds of the DNX, and switch between them, you n
 
 The easiest way to get started on Windows is to grab the latest preview of Visual Studio 2015, which can be found [here](http://go.microsoft.com/fwlink/?LinkId=521794).
 
-Visual Studio will install DNVM for you, so if you open a command prompt and type `dnvm` you should get some help text.
+Visual Studio will install DNVM for you, so if you open a developer command prompt and type `dnvm` you should get some help text.
 
 ### Upgrading DNVM or running without Visual Studio