Release process improvements

Release process improvements

While doing the 0.14 release I ran into a few minor issues when running the
scripts in contrib/release:
- The script contrib/release/upload-release.sh requires a version argument,
  but the version can just be read from the VERSION file.
- The contrib/release/do-release.sh does not do the git push.  I used
  my usual push script which also does a git rebase --ignore-date, which meant
  the commit got updated and the tag no longer referred to the commit.

Also, I realized it could be useful to have a release checklist to go through.

So:
- Use $(cat VERSION) in contrib/release/upload-release.sh to get version
- Add git push commands to contrib/release/do-release.sh
- Add README.release-checklist

2021-03-08  Tom de Vries  <tdevries@suse.de>

	* README.release-checklist: New file.
	* contrib/release/do-release.sh: Add git push commands.
	* contrib/release/upload-release.sh: Use $(cat VERSION) to get version.