Add page about users

[pascalduez]

Companies, open source projects, etc.

FT, Gardian?, BBC?, Salesforce, Oddbird, Phase2, Zurb, Lonely Planet, thoughbot...

https://libraries.io/npm/sassdoc/dependents
https://libraries.io/npm/sassdoc/dependent-repositories

https://github.com/ubuntudesign/vanilla-framework