Update the role distance filter

Currently the docs state that just `address` and `radius` which are incorrect, also there is no example




Proposed solution:

```
https://secure.tutorcruncher.com/api/contractors/?
distance_address=The+Food+Exchange%2C+New+Covent+Garden+Market%2C+Nine+Elms%2C+London+SW8+5EL%2C+ENGLAND&distance_radius=1
```


it is updated on the client just not the contractor