Add a beep script to notify a command is done

What does this MR do and why?

Source: https://gitlab.com/godfat/dev-tool/-/blob/master/bin/beep

Use this command to wrap around the command you would like to run, and then after it's finished, it'll tell you it's done. For example:

beep bundle install
bundle install; rails db:migrate; beep
beep bundle exec rspec spec/dot_gitlab_ci/rules_spec.rb

To configure this for iTerm2, follow:

Settings -> Profiles (and select your profile) -> Advanced
Look for "Triggers", and click on "Edit", and add a new trigger:

    Regular expression: \a
    Action: Bounce Dock Icon
    Parameters: Bounce Once
    Instant: check
    Enabled: check