Document workflows in a new `WORKFLOW.md` file

[maximearmstrong]

Feature request

Is your feature request related to a problem? Please describe. As discussed here, END_TO_END.md was deleted because it was outdated. By deleting that file, only our acceptance_test.yml workflow is now documents - our other workflows are not documented in the docs folder.

Proposed solution Adding a file WORKFLOW.md describing our workflows, like test_pack_doc.yml and end_to_end.yml, would be useful to users seeking more information.

This file could cover:

• The purpose of the workflows
• The expected behavior
• Common issues