so instead of

    git co master
    git merge --no-ff feature/my_feature
    git push github
    git push heroku

    git co master
    git merge --no-ff feature/my_feature
    git push github

Also, you could deploy to heroku as the result of merging a pull request through the github web-ui (if you're into that kind of thing).

Isn't this so that someone can just keep Github up to date and they don't need to use the CLI and do `heroku push` or whatever every time there is an update?

We use Microsoft Azure for some public sites, and there is both Github and BitBucket integration where you can automatically deploy updates to certain branches (e.g. `master` or `develop`) to the site.