Document manual QA testing steps

Document a set of procedures that can be used to perform a manual sanity check that the client is working as expected after a QA deployment. At a minimum this should include creating an annotation on an HTML and a PDF document. This is intended as a precursor to some kind of automated E2E test.

Context: In the frontend developer sync on 2021-03-03 an issue was raised that not everyone on the team was clear what/how to test for a manual sanity test on QA and in particular how to test the PDF.js integration on QA.