Add Zendesk

Adding Zendesk. http://www.zendesk.com/

Contributor: Kenshiro Nakagawa, Software Engineer (twitter & github @kencheeto)
Source: internal headcount

8 of 45 engineers from all Engineering teams (product development, ops, infra, QA, etc) located in San Francisco.
Merge pull request #43 from kencheeto/patch-1

Add Zendesk