Add code sponsor placement.

Author: jaredhanson

README.md

@@ -122,3 +122,5 @@ and [other](http://jaredhanson.net/pay) methods.  Any amount is appreciated.
 [The MIT License](http://opensource.org/licenses/MIT)
 
 Copyright (c) 2011-2016 Jared Hanson <[http://jaredhanson.net/](http://jaredhanson.net/)>
+
+<a target='_blank' rel='nofollow' href='https://app.codesponsor.io/link/vK9dyjRnnWsMzzJTQ57fRJpH/jaredhanson/passport-oauth2'>  <img alt='Sponsor' width='888' height='68' src='https://app.codesponsor.io/embed/vK9dyjRnnWsMzzJTQ57fRJpH/jaredhanson/passport-oauth2.svg' /></a>