[bug 1089650] Add a contribute.json file

Instead of asking all the usual questions like "Where is the code?",
"Where is the staging server?", "Do we have a mailing list?" you can
simply look all this up in the /contribute.json file.
This is great. One thing we could also do here is make sure that running `json.loads()` on the `resp.content` doesn't kick up an exception. That's a good way to also verify that the JSON is valid.