First impressions sweep of the overview index.html page.

Made usage of <strong> and <a> tags when referencing tags more constant. Added &raquo; to section links to make link into more of a call to action.
Edited top and bottom of Overview page.

Cut out words in the top for brevity. Added more reasons why someone would want to use DevTools to the top. Fixed some typos and links at the bottom.
Merge pull request #60 from pearlchen/overview-edits

Overview edits