Introduction: edits to Further Resources
Introduction: edits to Further Resources

- removed links to support.mapbox.com as we are phasing out the
  knowledge base and this is mentioned at /help
- added information about recommended third-party software &
  documentation

florianf/tileoven,tizzybec/tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,MappingKat/tilemill,fxtentacle/tilemill,florianf/tileoven,nyimbi/tilemill,tizzybec/tilemill,tilemill-project/tilemill,fxtentacle/tilemill,fxtentacle/tilemill,fxtentacle/tilemill,nyimbi/tilemill,tizzybec/tilemill,MappingKat/tilemill,paulovieira/tilemill-clima,tilemill-project/tilemill,florianf/tileoven,mbrukman/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Zhao-Qi/tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,Teino1978-Corp/Teino1978-Corp-tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,paulovieira/tilemill-clima,fxtentacle/tilemill,mbrukman/tilemill,Zhao-Qi/tilemill,MappingKat/tilemill,mbrukman/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,paulovieira/tilemill-clima,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill,nyimbi/tilemill,MappingKat/tilemill,MappingKat/tilemill,mbrukman/tilemill,Zhao-Qi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,tilemill-project/tilemill,tizzybec/tilemill