fixes bug 1058283 - Make a contribute.json endpoint

Dear ANYONE on the Socorro team, 
please have a look at the new contribute.json file. If you see anything missing or incorrect please say. 

The file [validates](https://contribute.paas.allizom.org/https%253A%252F%252Fraw.githubusercontent.com%252Fpeterbe%252Fsocorro%252Fdf9009fd4860d566a8be0678816c1ea947243fed%252Fcontribute.json) which is a good start. 
Aha! I guess that's because it's *mine*. I thought, since it had a list_id anybody could use it.