Update documentation for Test Coverage

[Sophietn]

Could be documented in a markdown called tests.md
Should document evidence of any tests, including automated tests we did before v1 release / continue to do before publishing new versions

[Sophietn]

@danuw are you working on this one? When do you think it could be ready by?

[Sophietn]

@vaughanknight and @danuw to cover this in the 1:1 tomorrow 7th Feb