The aws-cli installation documentation says to install completion for bash to run `complete -C aws_completer aws`. I looked at the `git` formula and tried to follow the use of `bash_completion.install`, but couldn't get it to work. So instead I have the caveat that tells the user to add `complete -C aws_completer aws` to their .bashrc. I don't know whether it is possible to do this automatically within the formula install method. If not I'll remove the comments.