[docs] Add http://www.gorillatoolkit.org/pkg/mux to README.

README.md

@@ -3,6 +3,8 @@ mux
 [![GoDoc](https://godoc.org/github.com/gorilla/mux?status.svg)](https://godoc.org/github.com/gorilla/mux)
 [![Build Status](https://travis-ci.org/gorilla/mux.svg?branch=master)](https://travis-ci.org/gorilla/mux)
 
+http://www.gorillatoolkit.org/pkg/mux
+
 Package `gorilla/mux` implements a request router and dispatcher.
 
 The name mux stands for "HTTP request multiplexer". Like the standard `http.ServeMux`, `mux.Router` matches incoming requests against a list of registered routes and calls a handler for the route that matches the URL or other conditions. The main features are: