docker-exec: add new example (#4818)

* docker-exec: add new example

* docker-exec: fix options format

pages/common/docker-exec.md

@@ -5,20 +5,24 @@
 
 - Enter an interactive shell session on an already-running container:
 
-`docker exec -it {{container_name}} {{/bin/bash}}`
+`docker exec --interactive --tty {{container_name}} {{/bin/bash}}`
 
 - Run a command in the background (detached) on a running container:
 
-`docker exec -d {{container_name}} {{command}}`
+`docker exec --detach {{container_name}} {{command}}`
 
 - Select the working directory for a given command to execute into:
 
-`docker exec -it -w {{path/to/directory}} {{container_name}} {{command}}`
+`docker exec --interactive -tty --workdir {{path/to/directory}} {{container_name}} {{command}}`
 
 - Run a command in background on existing container but keep `stdin` open:
 
-`docker exec -i -d {{container_name}} {{command}}`
+`docker exec --interactive --detach {{container_name}} {{command}}`
 
 - Set an environment variable in a running bash session:
 
-`docker exec -it -e {{variable_name}}={{value}} {{container_name}} {{/bin/bash}}`
+`docker exec --interactive --tty --env {{variable_name}}={{value}} {{container_name}} {{/bin/bash}}`
+
+- Run a command as a specific user:
+
+`docker exec --user {{user}} {{container_name}} {{command}}`