Clarify comment on rule evaluation
Clarify comment on rule evaluation

Fixes #1866
tattsun/prometheus,amorken/prometheus,brancz/prometheus,kzittritsch/prometheus,dmilstein/prometheus,AlekSi/prometheus,prometheus/prometheus,Colstuwjx/prometheus,AlekSi/prometheus,slok/prometheus,ton31337/prometheus,GoogleCloudPlatform/prometheus,msiebuhr/prometheus,tattsun/prometheus,sudhi-vm/prometheus,gottwald/prometheus,PrFalken/prometheus,adamron1/prometheus,kangwoo/prometheus,kangwoo/prometheus,alileza/prometheus,brancz/prometheus,tomwilkie/prometheus,JavierZunzunegui/prometheus,keegancsmith/prometheus,agaoglu/prometheus,gottwald/prometheus,PrFalken/prometheus,Conorbro/prometheus,kangwoo/prometheus,tomwilkie/prometheus,msiebuhr/prometheus,datajet-io/prometheus,amorken/prometheus,Gouthamve/prometheus,JavierZunzunegui/prometheus,msiebuhr/prometheus,Colstuwjx/prometheus,Stackdriver/stackdriver-prometheus,dsymonds/prometheus,agaoglu/prometheus,PrFalken/prometheus,SaltedMan/prometheus-annotated,datajet-io/prometheus,dmilstein/prometheus,tattsun/prometheus,alileza/prometheus,sudhi-vm/prometheus,keegancsmith/prometheus,slok/prometheus,gottwald/prometheus,brancz/prometheus,prometheus/prometheus,SaltedMan/prometheus-annotated,SaltedMan/prometheus-annotated,JavierZunzunegui/prometheus,tomwilkie/prometheus,sudhi-vm/prometheus,ton31337/prometheus,amorken/prometheus,agaoglu/prometheus,Conorbro/prometheus,Conorbro/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,Colstuwjx/prometheus,keegancsmith/prometheus,kzittritsch/prometheus,Gouthamve/prometheus,yanghongkjxy/prometheus,dsymonds/prometheus,GoogleCloudPlatform/prometheus,dsymonds/prometheus,AlekSi/prometheus,Conorbro/prometheus,amorken/prometheus,slok/prometheus,Gouthamve/prometheus,prometheus/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,tomwilkie/prometheus,AlekSi/prometheus,alileza/prometheus,gottwald/prometheus,tattsun/prometheus,datajet-io/prometheus,adamron1/prometheus,msiebuhr/prometheus,ton31337/prometheus,yanghongkjxy/prometheus,dmilstein/prometheus,PrFalken/prometheus,dsymonds/prometheus,prometheus/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,kangwoo/prometheus,ton31337/prometheus,kzittritsch/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,Colstuwjx/prometheus,adamron1/prometheus,SaltedMan/prometheus-annotated,sudhi-vm/prometheus,Stackdriver/stackdriver-prometheus,dmilstein/prometheus,slok/prometheus,kzittritsch/prometheus,yanghongkjxy/prometheus,adamron1/prometheus,datajet-io/prometheus,JavierZunzunegui/prometheus,yanghongkjxy/prometheus,agaoglu/prometheus,Gouthamve/prometheus,brancz/prometheus