[MacPorts] #36957: Guide: Document the "subport" command

[MacPorts]

#36957: Guide: Document the "subport" command
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  Reporter:  dave@…       |      Owner:  mascguy
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  guide        |    Version:
Resolution:               |   Keywords:
      Port:               |
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Changes (by mascguy):

 * owner:  macports-tickets@… => mascguy
 * cc: mascguy (removed)
 * status:  new => assigned


Comment:

 It looks like @JDLH provided a very nice draft write-up for `subport`, in
 a subsequent reply to the thread:

 https://lists.macports.org/pipermail/macports-dev/2021-July/043629.html

 Unfortunately there were no replies. But based on a quick read-through, it
 looks pretty good!

 I'll run with that, and submit a PR for review and feedback. A link will
 be added in a subsequent comment in this ticket, once it's been created.

-- 
Ticket URL: <https://trac.macports.org/ticket/36957#comment:22>
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