Document how to run our unit tests locally

[willmot]

Developers should be running unit tests locally before submitting changes, we need to document how they can do that. The wiki would be a good place to start.

[willmot]

Also document how to run them on windows (or at least link to it).

[willmot]

@dashaluna fancy documenting this alongside getting them running locally?

[dashaluna]

@willmot I need to do that.. so will start writing things down when I get to it. However, it will be for mac :) Will need some help with windows, will ask others.