Add access_log_format to config example (benoitc#1251)

The example given is the current default log format.

examples/example_config.py

@@ -147,6 +147,7 @@
 errorlog = '-'
 loglevel = 'info'
 accesslog = '-'
+access_log_format = '%(h)s %(l)s %(u)s %(t)s "%(r)s" %(s)s %(b)s "%(f)s" "%(a)s"'
 
 #
 # Process naming