add a contribute.json file (bug 1074452)

I did my best to find all the data to populate the json file, but l'm assuming I'll need to make a change or two. 
Now you have all these URLs repeated in two places in the repo. 
Perhaps it's just good enough to check that it's valid JSON and that it has the required keys. 
E.g.
```python
content = json.loads(response.content)
self.assertTrue(content['name'])
self.assertTrue(content['description'])
self.assertTrue(content['repository'])
```