Add Google Page Speed Insights as bot.yml

The user agent is:
"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.8 (KHTML, like Gecko; Google Page Speed Insights) Chrome/19.0.1084.36 Safari/536.8"
(http://stackoverflow.com/questions/16403295/what-is-the-name-of-the-google-pagespeed-user-agent)