adds contents for `Group`.
adds contents for `Group`.

* ISSUE
    - `access-control.md` does not have contents about `Group`

* SOLUTION
    - The contents are added to the file.

Private-issue: 1381

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