How to use page: Rework section that describes how to define owners
How to use page: Rework section that describes how to define owners

* Link to user guide and drop redundant information.
* Move this section to the end, as defining code owners is not supported
  in the UI and it looks displaced in the middle of the UI description.

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: Ifd1cb83a4faeb426c4901a643e1ebec4687961e7

GerritCodeReview/plugins_code-owners,GerritCodeReview/plugins_code-owners,GerritCodeReview/plugins_code-owners,GerritCodeReview/plugins_code-owners