[python-committers] Please edit the commit message when merge a PR

[Serhiy Storchaka]

When a PR is consistent on several commits, the final commit message 
composed by GitHub contains messages of all these commits: "fix typo", 
"address yyy comments", "revert zzz". If the initial commit message 
contained errors (e.g. absent issue number), it is easy to edit the 
title and text of a PR, but the initial commit message lefts unchanged. 
GitHub allows to edit the commit message of squashed commit, and please 
don't ignore this possibility. Otherwise the commit message in the 
repository will be ugly if not worse.