Mention rule priority system in Syntax Help and Clearance Report.

Fixes https://gitlab.com/kicad/code/kicad/issues/5647

pcbnew/dialogs/panel_setup_rules_help.txt

@@ -49,7 +49,11 @@ pad          hole        graphic         text             zone
 
 # ---- Notes
 #
-# Version clause must be first clause in file.
+# Version clause must be the first clause.
+#
+# Rules should be ordered by specificity.  Later rules take
+# precedence over earlier rules; once a matching rule is found
+# no further rules will be checked.
 #
 # Use Ctrl+/ to comment or uncomment line(s).
 #

pcbnew/drc/drc_engine.cpp

@@ -537,7 +537,7 @@ DRC_CONSTRAINT DRC_ENGINE::EvalRulesForItems( DRC_CONSTRAINT_TYPE_T aConstraintI
                 if( rcons->condition->EvaluateFor( a, b, aLayer, aReporter ) )
                 {
                     REPORT( implicit ? _( "Constraint applicable." )
-                                     : _( "Rule applied." ) )
+                                     : _( "Rule applied.  (No further rules will be checked.)" ) )
 
                     constraintRef = &rcons->constraint;
                     break;