Update backward compatibility notes for 0.8.0
Update backward compatibility notes for 0.8.0

Add a section to describe that country codes are required.

bloodybear/yona,ahb0327/yobi,ahb0327/yobi,oolso/yobi,ihoneymon/yobi,yona-projects/yona,oolso/yobi,Limseunghwan/oss,brainagenet/yobi,naver/yobi,doortts/forked-for-history,bloodybear/yona,oolso/yobi,Limseunghwan/oss,doortts/forked-for-history,brainagenet/yobi,bloodybear/yona,doortts/forked-for-history,doortts/fork-yobi,naver/yobi,naver/yobi,ahb0327/yobi,ihoneymon/yobi,doortts/fork-yobi,ihoneymon/yobi,yona-projects/yona,doortts/fork-yobi,yona-projects/yona,brainagenet/yobi,bloodybear/yona,doortts/fork-yobi,Limseunghwan/oss,yona-projects/yona