Create docs for how to test and debug in Talkilla

We need some documentation for how to test and debug in Talkilla. This is the start of some documentation.

The test document is an extension of what we already have, aimed at providing basic information on how to run the tests. We may want to point to test suite documentation in the future, but we can improve as we go.

The debugging document aims to be an outline of the major items we already use, and generally points to developer.mozilla.org where possible or for more information.

I suspect this will evolve over time, I want to provide a minimal baseline to help aid contributors or those working with our code base to get started.