Docs: add test framework info

[benilovj]

This extra documentation

• should help users get started with FitNesse
• can be referenced in the changes made as part of 'execute procedure' documentation improvements #188

[javornikolov]

Regarding test failure behaviour: I think I had some issues with setup=create some teables, teardown=drop them. If there is some exception/failure in test itself: the test tables were not dropped (so needed manual cleanup). Maybe that applies to some internal errors, but I'm not sure. (I'll share details if I manage to reproduce).

[benilovj]

If that's the case, it sounds like a bug in FitNesse (unless of course the DbEnvironment gets into a broken state). My understanding was that FitNesse continues on no matter what.

[javornikolov]

I have to try to reproduce it - I'm not sure what exactly was the case (but I think it happened when I create test incrementally and run it with setup but missing drop table at the end).

[javornikolov]

I did a few experiments and I couldn't invent an edge case which break the normal flow.

This looks good for merging to me 👍

[benilovj]

Thanks