It would be really nice, if support for git notes would be added. See this Blog post for an explanation.

You should add the functions GetNote(), SetNote(text) and RemoveNote() to a Commit.

Git notes are technically just files in the notes/commits ref. Try it yourself:

git init
git add --all
git commit --allow-empty -m "Test"
git notes add -m "This is a Note"
git checkout notes/commits

You should now see a file named after your commit which contains the Note.