Add note on how to mock to the docs

[darrenburns]

We need a page in the docs that tell users that to mock they should use from unittest import mock.

We should note that the mock.patch decorators don't currently work, and that we need to use the context managers instead.

[harshlancer]

If the issue is still relevant I'd like to contribute .@darrenburns

[darrenburns]

It's still relevant so feel free to open a PR, thanks!

[RamonGiovane]

Yes, it's indeed relevant, I wish to know what is the official way of using mocks with Ward.

[sarkartanmay393]

I want to contribute to this issue. Assign me this issue.