style.css: Fix font stack (missing family declaration)

We were missing the family declaration, so if a visitor didn't have
Open Sans installed the computer would substitute it with an undefined
font.  If we at least specify the family then the result should be
a bit more predictable.
Merge pull request #6 from alanorth/font-stack

style.css: Fix font stack (missing family declaration)
Merge pull request #7 from kkingori/master

Add Disqus comments for posts.