doc: add link to rejected addition of RequireSingleLineMethodSignature in upstream (#84)

Author: simPod

src/Cdn77/ruleset.xml

@@ -77,6 +77,7 @@
     <rule ref="SlevomatCodingStandard.Classes.ParentCallSpacing"/>
     <rule ref="SlevomatCodingStandard.Classes.PropertySpacing"/>
     <rule ref="SlevomatCodingStandard.Classes.RequireConstructorPropertyPromotion" />
+    <!-- Not accepted in upstream https://github.com/doctrine/coding-standard/pull/280 -->
     <rule ref="SlevomatCodingStandard.Classes.RequireSingleLineMethodSignature"/>
     <rule ref="SlevomatCodingStandard.ControlStructures.JumpStatementsSpacing">
         <properties>