ENH: Copy release merge commit message to git tag message

[westurner]

(Maybe an option to) by default,
copy the release merge commit message to the git tag message.
so that GitHub Releases have the relevant commit message [first lines?]

To publish a tag as a GitHub Release:

• View the releases: https://github.com/datasift/gitflow/releases
• Click the release tag
• Click 'Edit Tag' (e.g. https://github.com/datasift/gitflow/releases/new?tag=0.1.0 )
• Click 'Publish Release'