[pkg] Warn about "develop" command not installing legacy cubes directory
Not sure we can do better than a warning, which is better than nothing
anyways.
Closes #15785635.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/html/index.html
Files: /usr/share/doc/cubicweb-documentation/html/*