GitHub: change default commit message

[hugovk]

Can we change the default commit message from the "default message":

To the "pull request title"?

This means instead of getting commit messages like "Merge pull request #8913 from hugovk/sphinx-autobuild", which aren't very useful:

We get something more descriptive like "Add make [-C docs] htmllive to rebuild and reload HTML files (#8913)":

@aclark4life The settings are at https://github.com/python-pillow/Pillow/settings

[hugovk]

On the topic of commit messages, we currently have a bit of a mix, but I also recommend using the imperative mood for commits and PR titles:

https://cbea.ms/git-commit/?featured_on=pythonbytes#imperative

For example:

Add make [-C docs] htmllive to rebuild and reload HTML files

And not past tense:

Added make [-C docs] htmllive to rebuild and reload HTML files

[aclark4life]

Done!

[hugovk]

Thanks!