adding mailing list and Lighthouse links to README
adding mailing list and Lighthouse links to README

janusnic/clearance,benlivermore/clearance,thoughtbot/clearance,thoughtbot/clearance,pedrosmmoreira/clearance,janusnic/clearance,pedrosmmoreira/clearance,naveed-ahmad/clearance,naveed-ahmad/clearance,crowdtap/clearance,zernie/clearance,rubyist/clearance,janusnic/clearance,zernie/clearance,sferik/clearance,naveed-ahmad/clearance,benlivermore/clearance,crowdtap/clearance,benlivermore/clearance,zernie/clearance,pedrosmmoreira/clearance,openeducation/clearance,thoughtbot/clearance,crowdtap/clearance,rubyist/clearance