How do you assign a keyboard shortcut to an Automator workflow?

This has to be an incredibly basic question, but my searches haven't turned up anything.

I created an Automator workflow to "Create new email message".

I'd like to be able to launch this with a keyboard shortcut.

In System Preferences, I can see how to assign keyboard shortcuts to menu items, but can't figure how how/if you can do this for automator shortcuts.

Thanks.