Add scrutinizer badge

Signed-off-by: Michal Čihař <michal@cihar.com>

README.rst

@@ -25,6 +25,11 @@ Code coverage:
 .. image:: https://coveralls.io/repos/phpmyadmin/phpmyadmin/badge.png?branch=master
     :target: https://coveralls.io/r/phpmyadmin/phpmyadmin?branch=master
 
+Code quality:
+
+.. image:: https://scrutinizer-ci.com/g/phpmyadmin/phpmyadmin/badges/quality-score.png?s=93dfde29ffa5771d9c254b7ffb11c4e673315035
+    :target: https://scrutinizer-ci.com/g/phpmyadmin/phpmyadmin/
+
 Download
 --------