Update README with basic info about offline testing

[lenarother]

Hi @EnTeQuAk ,

I am interested in your solution for #5 and what is the cleanest way of testing.
So far I updated the READMY with mock solution which worked for me.

Best,
Magdalena

[EnTeQuAk]

Thanks for the patch @lenarother and sorry that I didn't see this earlier. I'll look into the failing test (which is because django 1.6 and we don't really support that anymore) so we can get this change into master.

I don't have a solution for #5 yet but expect some more work on it a bit later.

Thanks!

[EnTeQuAk]

I'm going to merge this, the failing tests don't matter on master since we don't test on 1.6 and 1.7 anymore.

[EnTeQuAk]

Thanks again for the patch!