Flesh out the documentation for datagrids.

Review Request #7391 — Created June 8, 2015 and submitted — Latest diff uploaded

Information

Djblets
release-0.9.x
e7ba306...

Reviewers

The datagrid documentation needed to be updated a bit. This fleshes it
out with more details, and provides a short summary at the top of the
page.

Viewed the docs. Looked as expected.