Add instructions for installing the express3 version of everyauth. (Closes GH-274)

Author: bnoguchi

README.md

@@ -85,8 +85,15 @@ So far, `everyauth` enables you to login via:
 
 
 ## Installation
+
+If you are using Connect 1.x or Express 2.x, install via:
+
     $ npm install everyauth
 
+If you are using Express 3.x, install via:
+
+    $ npm install git://github.com/bnoguchi/everyauth.git#express3
+
 ## Quick Start
 Using everyauth comes down to just 2 simple steps if using Connect
 or 3 simple steps if using Express: