Add Source Sans Pro from Google Web fonts

Added web font `link` element in the `head` element right after the charset.

Google instructs to add the `link` element as the first element in `head`, but I've read that charset `meta` tag should be always the first one. That's why I put the `link` right after charset.

According to this SA answer (http://stackoverflow.com/questions/12316501/including-google-web-fonts-link-or-import), using `link` instead of `@import` is the way to go.