pkg/54015: Guide does not document stable directory in FTP server layout appendix

[jlmuir%imca-cat.org@localhost]

>Number:         54015
>Category:       pkg
>Synopsis:       Guide does not document stable directory in FTP server layout appendix
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Feb 25 23:15:00 +0000 2019
>Originator:     J. Lewis Muir
>Release:        
>Organization:
>Environment:
>Description:
At

  https://www.netbsd.org/docs/pkgsrc/ftp-layout.html

it documents all the directories except one: stable.
>How-To-Repeat:

>Fix:
Add a section documenting the stable directory.