Add Gitter badge to README
Add Gitter badge to README

k0kubun/byebug,deivid-rodriguez/byebug,deivid-rodriguez/byebug,yui-knk/byebug,deivid-rodriguez/byebug,guilherme/byebug,guilherme/byebug,k0kubun/byebug,yui-knk/byebug,guilherme/byebug,yui-knk/byebug,k0kubun/byebug