added gitter link to docs
added gitter link to docs

chrinide/optunity,MarkAWard/optunity,chrinide/optunity,claesenm/optunity,MarkAWard/optunity,claesenm/optunity,MarkAWard/optunity,claesenm/optunity,chrinide/optunity,chrinide/optunity,MarkAWard/optunity,claesenm/optunity