Add a description on multiple filter matches into the documentation
Add a description on multiple filter matches into the documentation

The description of how multiple filter matches work was missing in the
documentation. This change inserts the missing description into the
documentation.

Change-Id: I6643ae920938faa9cfa5661d8f2f04ae7906ae58

GerritCodeReview/plugins_reviewers,davido/gerrit-reviewers-plugin,GerritCodeReview/plugins_reviewers,davido/gerrit-reviewers-plugin,GerritCodeReview/plugins_reviewers