Hello Nick
What kind of like are you interested in? The following page will show you how you can add a Facebook like button: https://developers.facebook.com/docs/plugins/like-button
In this case, you can add a like button as an iframe, and this will work in the editor and if the recipient clicks the "view in browser" button, but the iframe will not display within email clients. There is also a "like url" option which will allow you to make text or an image serve as a like button (this works in email clients, but opens a separate page that says that the person that clicked the link 'liked' whatever it was).
