Add example

Php-mess-detector-plugin.md

@@ -5,4 +5,17 @@ Runs PHP Mess Detector against your build. Records some key metrics, and also re
 * **suffixes** - Optional - An array of file extensions to check.
 * **ignore** - Optional - An array of files/paths to ignore, defaults to the build_settings ignore list.
 * **path** - Optional - Directory in which PHPMD should run.
-* **rules** - Optional - Array of rulesets that PHPMD should use when checking your build or a string containing at least one slash, will be treated as path to PHPMD ruleset.
+* **rules** - Optional - Array of rulesets that PHPMD should use when checking your build or a string containing at least one slash, will be treated as path to PHPMD ruleset.
+
+
+### Example config:
+
+```yml
+php_mess_detector:
+    rules: 
+        - "codesize"
+        - "unusedcode" 
+        - "naming"
+        - "somedir/customruleset.xml"
+    allow_failures: true
+```