Update of Github Page (And don't forget we have joint meeting today at 11am EDT)

Hi folks

I just updated our github page (Yeah we do have one)
https://w3c.github.io/publishingcg/ and added a few useful links in the
middle of left nav bar pointing to latest epub 33 specs and link to test
suites.

The github page has more flexibility than the w3c official community page (
https://www.w3.org/community/publishingcg/) which we could not make change.
And it can have more rich than a single markdown.  So we will add more blog
like stuff there in github page. The update is still ongoing (I plan to add
links to our Task Force works) please feel free to let us know what you
would like to add to it.

Cheers,
Zheng