Moving details about how the docs are built into a separate doc, allowing `documenting.rst` to focus on guidance for how to document passes/cells (and what the help text should contain).
Also puts cell help v2 and `Pass::formatted_help` as the primary means of providing help text, with the older styles being pseudo deprecated (or at least depreciated), reframing them as the more limited original methods rather than the default (despite functionally being that).
Still very much WIP.
af93a0cfc9