Added legend element to checklist

The legend explains to screen-readers what the group of fields is about. Especially important for groups of checkboxes or radio buttons, as the legend will be the question that the checkboxes or radio buttons are answers for. "The first element inside the fieldset must be a legend element, which provides a label or description for the group" - http://www.w3.org/TR/2012/NOTE-WCAG20-TECHS-20120103/H71
Merge pull request #175 from keeganstreet/patch-1

Added legend element to checklist
Changed main area from section to div

Hi, what do people think about changing the recommendation for the main content area to be a div instead of a section?

Bruce Lawson talks about this exact thing at http://html5doctor.com/the-section-element/

"What we’ve been doing wrong is using section to ... demarcate the main content area from the nav, header, footer etc. These are jobs for div, not section."
Merge pull request #176 from keeganstreet/patch-1

Changed main area from section to div for checklist
Adds main tag to checklist
Persistent checklist. Resolves issue #15
Browsing enhancements
Fixing botched merge
Resource tweaks
Update alt-text.md with ideas from Issue #177

Merge my article with the actual alt text article.
Merge pull request #180 from p4bl1t0/patch-1

Update alt-text.md with ideas from Issue #177