Consisently use /run vice /var/run for documentation and init system integration

etc/dkimpy-milter.conf

@@ -38,7 +38,7 @@ Socket			inet:8892@localhost
 ###  Name of the file where the filter should write its pid before beginning
 ###  normal operations.
 #
-PidFile			/var/run/dkimpy-milter/dkimpy-milter.pid
+PidFile			/run/dkimpy-milter/dkimpy-milter.pid
 
 ##  Userid userid
 ###      default dkimpy-milter