Bug 247506

Adapting that example to my ports layout (/usr/ports empty and svn co of ports tree under ~/ports for ease of port maintenance) gives me:

% sudo poudriere ports -c -F f none -M ~/ports -p libudisks
[00:00:00] Error: Directory not empty at /home/pauamma/ports

After staring at the poudriere-ports manpage a bit, I tried:
% sudo poudriere ports -c -m null -M ~/ports -p libudisks
[00:00:00] Imported ports tree "libudisks" from /home/pauamma/ports

The rest of the port testing sequence proceeded without incident, so I assume that command was OK, so I'd like to use it instead of the erroring command for the handbook, on the grounds that it's really counterintuitive to have a "directory must only be populated *after* issuing this command" restriction at this point in the workflow implied by the handbook order. However, since I'm not a poudriere expert, I'd like one to comment on the proposed language change before I submit a Phabricator review. (Cc'd bdrewery@FreeBSD.org to that effect, on the grounds that they're the port maintainer and thus presumably know more about poudriere than I do.)