Updating "contribution Checklist" to recommend git format-patch.

[Florian Weimer]

On 06/26/2018 04:33 PM, Carlos O'Donell wrote:
> We should not require people to use git-show-gnu scripts, and
> all developers should have the Changelog merge helper to make
> it easy to commit such patches.

The merge helper only runs if Git knows the hash of the previous version 
of the ChangeLog file mentioned in the patch.  This means that the merge 
always fails if the patch was created from a ChangeLog file which has 
not been pushed to sourceware.org.  This is certainly a downside.

The upside is that we'd see what people intend to use as an author ID 
and commit message, which could be helpful in some cases.

I'm not quite sure yet how one thing weighs against the other.

Thanks,
Florian