[Hacktoberfest] Add and Update useful Docker commands

source/snippets/docker/index.md

@@ -107,17 +107,25 @@ docker image rm <image hash> //only first 3 characters of hash code is enough fo
 Docker containers
 ```bash
 // list all containers online/offline
-
 docker ps -a
 docker container ls -a
-// remove/stop/kill a certain container
 
+// remove/stop/kill a certain container
 docker kill rm <container hash>
-```
-//coming out of container without exiting it:  ctrl+P+Q
+
+//coming out of container without exiting it
+ctrl+P+Q
 
 //searching docker image on docker hub
 docker search <<image_name>>
 
 //tagging local image with another name
 docker tag <<old_image_name>> <<new_image_name>>
+
+//"SSH" into a running container
+docker exec -it <<container_name>> /bin/bash
+
+//Execute arbitrary command in container
+docker exec -it <<container_name>> <<command>>
+
+```