Display the page load time 

The plugin will generate a graph that displays the page load time
We need to add our custom log format into Apache config.
The plugin was tested on Ubuntu Server 12.04.02 LTS - munin version
1.4.6
LogFormat "%h %l %u %t \"%r\" %>s %O %b %D \"%{Referer}i\"
\"%{User-Agent}i\"" custom