Update README.md

To show bash profile step for osx

Author: MRdNk

README.md

@@ -47,6 +47,13 @@ brew tap aspnet/dnx
 brew update
 brew install dnvm
 ```
+
+Add dnvm to your bash profile (./bash_profile)
+```bash
+source dnvm
+```
+
+
 Note that on Windows the .NET Framework is already installed, whereas on OS X the brew formula uses a particular version of [Mono](http://www.mono-project.com/) that we know works with ASP.NET 5.
 
 ## Linux