[DOC] Add "Who is using it" section to website

[lukemelia]

This would allow prospective users of ember-cli-deploy to gain confidence in choosing it, as well has possibly highlight different styles of deployment people are using. Maybe we can incorporate an opportunity to link to company's opensource plugin-pack if they have one, and/or list the tech they are using. This could allow highlighting of people using deployjs to deploy non-ember apps, too.