added info and links for contributing data to home page, closes #152
added info and links for contributing data to home page, closes #152

UrbanCCD-UChicago/plenario,UrbanCCD-UChicago/plenario,tosseto/plenario,dssg/plenario,tosseto/plenario,UrbanCCD-UChicago/plenario,tosseto/plenario,dssg/plenario,dssg/plenario