Added Gitter account info to README
Added Gitter account info to README

Design-Collective/mailboxer,roomaroom/mailboxer,shekibobo/mailboxer,shekibobo/mailboxer,cantonyselim/mailboxer,mattherick/mailboxer,chepri/mailboxer,untitledstartup/mailboxer,modsaid/mailboxer,cantonyselim/mailboxer,modsaid/mailboxer,roomaroom/mailboxer,chepri/mailboxer,mattherick/mailboxer,joshtate04/mailboxer,t27duck/mailboxer,untitledstartup/mailboxer,sai43/mailboxer,jarkadlec/mailboxer,jason-wang-0401/mailboxer,lacco/mailboxer,Groovej/mailboxer,Design-Collective/mailboxer,techstars/mailboxer,joshtate04/mailboxer,lacco/mailboxer,div/mailboxer,t27duck/mailboxer,netbrick/mailboxer,mailboxer/mailboxer,jarkadlec/mailboxer,sai43/mailboxer,mailboxer/mailboxer,Groovej/mailboxer,netbrick/mailboxer,jason-wang-0401/mailboxer