more info about docker extension

Author: chrisdias

docs/languages/dockerfile.md

@@ -65,3 +65,17 @@ Visual Studio Code's experience for authoring `docker-compose.yml` is also very
 VS Code will first show a list of popular images along with metadata such as the number of stars and description. If you continue typing VS Code will query the Docker Hub index for matching images, including searching public profiles. For example, searching for `Microsoft` will show you all the public Microsoft images.
 
  ![Docker Compose Microsoft image suggestions](images/docker/dockercomposesearch.png)
+
+## Docker commands
+Many of the most common Docker and docker-compose commands are built right into the Command Palette (F1).
+
+![intelliSense](images/docker/dockercommands.gif)
+
+## Dockerfile linting
+You can enable linting of Dockerfile files through the `docker.enableLinting` setting (CMD+, on MacOS, or Ctrl+, on Windows and Linux). The extension uses the awesome [dockerfile_lint](https://github.com/projectatomic/dockerfile_lint) rules based linter to analyze the Dockerfile. You can provide your own customized rules file by setting the `docker.linterRuleFile` setting. You can find [more information](https://github.com/projectatomic/dockerfile_lint#extending-and-customizing-rule-files) on how to create rules files as well as [sample rules files](https://github.com/projectatomic/dockerfile_lint/tree/master/sample_rules) in the [dockerfile_lint](https://github.com/projectatomic/dockerfile_lint) project. 
+
+![linting](images/docker/dockerfilelinting.gif)
+
+## Running commands on Linux
+By default, Docker runs as the root user on Linux, requiring other users to access it with `sudo`. This extension does not assume root access, so you will need to create a Unix group called docker and add users to it. Instructions can be found here: [Create a Docker group](https://docs.docker.com/engine/installation/linux/ubuntulinux/#/create-a-docker-group)
+