site: add step manage-docker-as-a-non-root-user in the requirements o…

…f docker driver (#19925)

Signed-off-by: lubingtan <bingtanlu@gmail.com>

site/content/en/docs/drivers/docker.md

@@ -16,6 +16,7 @@ The Docker driver allows you to install Kubernetes into an existing Docker insta
 - [Install Docker](https://docs.docker.com/engine/install/) 18.09 or higher (20.10 or higher is recommended)
 - amd64 or arm64 system.
 - If using WSL complete [these steps]({{<ref "/docs/tutorials/wsl_docker_driver">}}) first
+- Don't forget to follow this [step](https://docs.docker.com/engine/install/linux-postinstall/#manage-docker-as-a-non-root-user) to manage Docker as a non-root user.
 
 ## Usage