update docker user permission

docker/README.md

@@ -88,4 +88,18 @@
 
   
 
-* s
+* user permission
+
+```shell
+// create docker group
+$ sudo groupadd docker
+
+// add current user to group
+$ sudo usermod -aG docker ${USER}
+
+// reboot system for group privillege to take effect
+
+// test run
+$ docker run hello-world
+
+```