Add a link to CQL help

I matched the opacity of the [JIRA help icon](https://hammerlab.atlassian.net/browse/DEMETER-30?jql=project%20%3D%20DEMETER):
![screen shot 2014-12-05 at 3 35 14 pm](https://cloud.githubusercontent.com/assets/98301/5322503/6e3e3ce8-7c94-11e4-9ee5-c0e2a8dd9ade.png)

The icon is a [public domain one](http://thenounproject.com/term/help/61692/) from the nouns project, so I don't believe we need to include any attribution.

Fixes #352