Added context text and fixed group label typos

Addresses the second item in #512 (closed)

Add explainer text that this is not all the work that the team do. Either link to handbook or list out what is not covered (OKRs, reactive MRs, community contributions, routine tasks, release post work ...).

Also fixes group label typos, adds context intro paragraphs from the 14.6 issue, and updates the dates by which we want to create the issue and add the links.