git: add coauthor alias

Author: branchvincent

.config/git/config.aliases

@@ -43,6 +43,7 @@
 
     # Commit
     amend = commit -q --amend --no-edit
+    coauthor = !git commit --amend --message=\"$(git log -1 --format=%B)\" --message=\"Co-authored-by: $(git config --get user.name) <$(git config --get user.email)>\"
     commit-each = "!f() { for fn in $(git ls-files --modified); do git commit -nm \"$(basename \"${fn%.*}\"): $1\" \"$fn\"; done; }; f"
     fixup = !git amend && git push -q --force-with-lease
     uncommit = reset --soft HEAD~1