Add one more doc link.

Author: timdorr

modules/RoutingContext.js

@@ -4,7 +4,7 @@ import warning from './warning'
 
 const RoutingContext = React.createClass({
   componentWillMount() {
-    warning(false, '`RoutingContext` has been renamed to `RouterContext`. Please use `import { RouterContext } from \'react-router\'.`')
+    warning(false, '`RoutingContext` has been renamed to `RouterContext`. Please use `import { RouterContext } from \'react-router\'`. http://tiny.cc/router-routercontext')
   },
 
   render() {