[MacPorts] #58097: carthage @0.31.2: add shell completions

[MacPorts]

#58097: carthage @0.31.2: add shell completions
--------------------------+-----------------------
  Reporter:  FranklinYu   |      Owner:  saagarjha
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  carthage     |
--------------------------+-----------------------

Comment (by saagarjha):

 Hang on, let me figure out how zsh and fish handle completion and I'll
 create a revision that fixes this.

-- 
Ticket URL: <https://trac.macports.org/ticket/58097#comment:2>
MacPorts <https://www.macports.org/>
Ports system for macOS