Add link to GitHub Pages.

Author: steveklabnik

README.md

@@ -9,3 +9,5 @@ $ ./serve.sh
 ```
 
 Then open a browser at [http://localhost:8000](http://localhost:8000).
+
+Alternatively, you can visit [http://json-api.github.io/browser/](http://json-api.github.io/browser/), hosted on GitHub Pages.