[MacPorts] #54605: Update guide to tell user where to get "original" Portfile for patching

[MacPorts]

#54605: Update guide to tell user where to get "original" Portfile for patching
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  Reporter:  jfcaron3  |      Owner:
      Type:  defect    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  guide     |    Version:
Resolution:            |   Keywords:
      Port:            |
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Comment (by jfcaron3):

 Those are both good suggestions.  One or both methods should be mentioned
 in the Portfile patches section of the Guide.

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Ticket URL: <https://trac.macports.org/ticket/54605#comment:3>
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