管理员指南中，管理用户，缺少用户组的管理

Is this a BUG REPORT or FEATURE REQUEST?: FEATURE REQUEST

Uncomment only one, leave it on its own line:

bug

feature

What happened:
仅提供用户的管理，未提供用户组的管理

What you expected to happen:
提供用户组的管理
How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

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@youwu88 将会做如下修改：
1、将章节名称修改为：管理用户和用户组
2、将章节目录修改为：
管理用户和用户组
管理用户
增加用户
修改用户帐户
删除用户
管理员帐户授权
管理用户组
增加用户组
修改用户组
删除用户组
将用户加入用户组和从用户组移除
切换用户组

openEuler / docs