Add overlay with mission statement/overview to landing page

[vallyre]

Landing page (home pg) does not reveal the site purpose/value without additional navigation. Would like to add an overlay, fixed to bottom of viewport, which contains a quick mission phrase and how to start using the tool. Would disappear upon 'dirty' search box to reveal full-screen map results.

Need to reformat map initialization latitude to be about 10 px to the north so "Durham" is higher on the page...