Arthas keymap 命令教程 (#1318)

* add keymap command scenario. #847

Signed-off-by: hollowman6 <hollowman186@vip.qq.com>

* fix link typo

Signed-off-by: hollowman6 <hollowman186@vip.qq.com>

* remove additional link

Signed-off-by: hollowman6 <hollowman186@vip.qq.com>

* polish 'Custom shortcuts'

Signed-off-by: hollowman6 <hollowman186@vip.qq.com>

* polish kaymap command scenario. #847

Signed-off-by: hollowman6 <hollowman186@vip.qq.com>

* fix mistake

Signed-off-by: hollowman6 <hollowman186@vip.qq.com>