README: Replace references to Redmine with Github Issues
README: Replace references to Redmine with Github Issues

Signed-off-by: Alistair Buxton <4a118229dd29fd86055ab812cdd2e4151d07a54f@gmail.com>

agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,leon-anavi/meta-raspberrypi,d21d3q/meta-raspberrypi,kraj/meta-raspberrypi,toolmmy/meta-raspberrypi,toolmmy/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,toolmmy/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,d21d3q/meta-raspberrypi,kraj/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,d21d3q/meta-raspberrypi,d21d3q/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,kraj/meta-raspberrypi,schnitzeltony/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,toolmmy/meta-raspberrypi