I did something similar to this a while back with a one-liner aliased in my Bash includes, called gitsum (short for git summary).

    alias gitsum='git log --pretty=format:"* %s" --author `git config user.email`' #myself

It gives my git commit messages as a Markdown bullet-point list. It only works per-branch unlike the linked gist, but one cool thing about it is that you can tack on additional git flags, such as --since. For example:

    gitsum --since 1.day
    gitsum --since 1.week
    gitsum --since 8.hours

I usually pipe this into my clipboard (on Mac) to easily paste it into the time logging or reporting system:

    gitsum --since 1.day | pbcopy