Document which factors are used to compute code owner scores
Document which factors are used to compute code owner scores

Users often ask about this, hence this information should be documented.
Also list factors that are not taken into account, but which are
frequently wanted, so that it's clear that these are currently not
supported.

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: Idfdf191198dece8e0bf15ba064d9e4fcdc2118d9

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