Add .editorconfig guidelines in the Contributor Guide documentation

Contributor Guide.html

@@ -137,7 +137,12 @@ <h3>Ensure All Tests Pass</h3>
 
 <h2>Submit a Pull Request</h2>
 
-Be sure to link to the JIRA issue in your GitHub pull request.  Also, go back to your JIRA issue and link to the pull request.
+<p>
+    Be sure to link to the JIRA issue in your GitHub pull request.  Also, go back to your JIRA issue and link to the pull request.
+</p>
+<p>We use tabs for code indentation, not spaces. As this is not the default in Visual Studio, you will need to reconfigure Visual Studio to indent with tabs whenever you work on the NHibernate codebase. To make this easier, NHibernate has an 
+    <a href="http://www.editorconfig.org/">editorconfig</a> configuration file to switch Visual Studio automatically between
+tabs and spaces mode. It is recomended you install editorconfig from the Visual Studio Extension Manager.</p>
 
 <h2>Further Discussion</h2>