Add documentation for the Owners tool

Summary:
As title.

Please help me to improve the wording!

Test Plan:
generate the documentation from the diviner file; read it; spell
check

Reviewers: epriestley, nh

Reviewed By: nh

CC: aran, dihde14, mpodobnik, prithvi, TomL, epriestley

Differential Revision: https://secure.phabricator.com/D1395