add extra note for CLI installation

Author: HomelessDinosaur

src/pages/reference/cli/installation.mdx

@@ -13,6 +13,12 @@ Please follow these links to the official installation steps for each.
 - [Docker Buildx](https://github.com/docker/buildx/)
 - [Pulumi](https://www.pulumi.com/docs/cli/) _(for deployments, only needed if using the default providers)_
 
+<Note>
+  When setting up docker on Linux be sure to follow the [post-installation
+  steps](https://docs.docker.com/engine/install/linux-postinstall/) so you can
+  run docker as a non-root user.
+</Note>
+
 ## Installing the Nitric CLI
 
 <CodeGroup>