Update QA Docs

[pietrop]

Is your feature request related to a problem? Please describe.

https://github.com/bbc/react-transcript-editor/pull/69

Describe the solution you'd like

Update the QA testing docs so that it can be used when doing substantial refactors

Describe alternatives you've considered

• ~Having less confidence in the changes and rolling the dice on new PRs~
• supplementing QA with some automated testing

Additional context

NA