Inplace import improvements (rebased)

Fix for https://trello.com/c/6Wv0H2Rk/126-better-explain-inplace-user-requirements - explaining extra user and group set-up needed for in-place imports.

--rebased-from #1022 (without the commit to fix typos which don't exist on this branch)
Example was pasted from https://trello.com/c/bxvMXqiy/447-group-write-on-dogfish with amendments by Kenny to remove the server address - I'm not going to mess with it now!