added documentation for .nvmrc usage

README.markdown

@@ -42,6 +42,10 @@ And then in any new shell just use the installed version:
 
     nvm use 0.10
 
+You can create an `.nmvrc` file containing version number in the project root folder; run the following command to switch versions:
+
+    nvm use
+
 Or you can just run it:
 
     nvm run 0.10