fyi: webperf homepage

[Philippe Le Hegaret]

I've been meaning for a long time to redo the webperf homepage and move 
it to GitHub. Folks can see my latest attempt at

   http://w3c.github.io/web-performance/
Should work good enough on all devices/platforms.

Once a few folks had a chance to see it, I'll replace the existing one. 
I still have some ideas for the content (such as using a twitter feed 
for the news section) but not sure when I'll get to it.

As usual, feedback on GitHub is welcome.

Philippe