[issue18384] Add devhelp build instructions to the documentation makefile (Python3)

[Balthazar Rouberol]

Changes by Balthazar Rouberol <brouberol at imap.cc>:


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title: Add devhelp build instructions to the documentation makefile -> Add devhelp build instructions to the documentation makefile (Python3)

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18384>
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