git: handle the case where `git tag` opens an editor

[midnightveil]

For me, the git tag bender-tmp-<commit> <commit> --force opens a nano process, which then causes the bender checkout to just hang wait for git to complete.

Add a message just to make it go on its merry way.

(An alternate solution would probably be to add --no-sign, as this is the cause in my specific case).

cc @niwis