[Oct 27, 2021, Universe] Dev container feature configuration (beta) (#22136)

* Update dev container config info

* Update feature availability

* Add image of addtl. features menu

Author: ethanpalm

assets/images/help/codespaces/select-additional-features.png

@@ -22,7 +22,9 @@ shortTitle: Configure your project
 
 ## About dev containers
 
-A development container, or dev container, is the environment that {% data variables.product.prodname_codespaces %} uses to provide the tools and runtimes that your project needs for development. When working with a dev container in {% data variables.product.prodname_codespaces %} you can either [use the default configuration](#using-the-default-configuration), [use a predefined configuration](#using-a-predefined-container-configuration), or [create your own configuration](#creating-a-custom-codespace-configuration). The option you choose is dependent on the tools, runtimes, dependencies, and workflows that a user might need to be successful with your project.
+A development container, or dev container, is the environment that {% data variables.product.prodname_codespaces %} uses to provide the tools and runtimes that your project needs for development. If your project does not already have a dev container defined, {% data variables.product.prodname_codespaces %} will use the default configuration, which contains many of the common tools that your team might need for development with your project. For more information, see "[Using the default configuration](#using-the-default-configuration)."
+
+If you want all users of your project to have a consistent environment that is tailored to your project, you can add a dev container to your repository. You can use a predefined configuration to select a common configuration for various project types with the option to further customize your project or you can create your own custom configuration. For more information, see "[Using a predefined container configuration](#using-a-predefined-container-configuration)" and "[Creating a custom codespace configuration](#creating-a-custom-codespace-configuration)." The option you choose is dependent on the tools, runtimes, dependencies, and workflows that a user might need to be successful with your project.
 
 {% data variables.product.prodname_codespaces %} allows for customization on a per-project and per-branch basis with a `devcontainer.json` file. This configuration file determines the environment of every new codespace anyone creates for your repository by defining a development container that can include frameworks, tools, extensions, and port forwarding. A Dockerfile can also be used alongside the `devcontainer.json` file in the `.devcontainer` folder to define everything required to create a container image.
 
@@ -79,17 +81,30 @@ The default configuration is a good option if you're working on a small project
 
 Predefined container definitions include a common configuration for a particular project type, and can help you quickly get started with a configuration that already has the appropriate container options, {% data variables.product.prodname_vscode %} settings, and {% data variables.product.prodname_vscode %} extensions that should be installed.
 
-Using a predefined configuration is a great idea if you need some additional extensibility. You can also start with a predefined configuration and amend it as needed for your project's setup. 
+Using a predefined configuration is a great idea if you need some additional extensibility. You can also start with a predefined configuration and amend it as needed for your project's setup.
 
 {% data reusables.codespaces.command-palette-container %}
 1. Click the definition you want to use.
   ![List of predefined container definitions](/assets/images/help/codespaces/predefined-container-definitions-list.png)
-1. Follow the prompts to customize your definition.
+1. Follow the prompts to customize your definition. For more information on the options to customize your definition, see "[Adding additional features to your `devcontainer.json` file](#adding-additional-features-to-your-devcontainerjson-file)."
 1. Click **OK**.
   ![OK button](/assets/images/help/codespaces/prebuilt-container-ok-button.png)
 1. To apply the changes, in the bottom right corner of the screen, click **Rebuild now**. For more information about rebuilding your container, see "[Applying changes to your configuration](#applying-changes-to-your-configuration)."
   !["Codespaces: Rebuild Container" in the command palette](/assets/images/help/codespaces/rebuild-prompt.png)
 
+### Adding additional features to your `devcontainer.json` file
+
+{% note %}
+
+**Note:** This feature is in beta and subject to change.
+
+{% endnote %}
+
+You can add features to your predefined container configuration to customize which tools are available and extend the functionality of your workspace without creating a custom codespace configuration. For example, you could use a predefined container configuration and add the {% data variables.product.prodname_cli %} as well. You can make these additional features available for your project by adding the features to your `devcontainer.json` file when you set up your container configuration.
+
+You can add some of the most common features by selecting them when configuring your predefined container. For more information on the available features, see the [script library](https://github.com/microsoft/vscode-dev-containers/tree/main/script-library#scripts) in the `vscode-dev-containers` repository.
+
+![The select additional features menu during container configuration.](/assets/images/help/codespaces/select-additional-features.png)
 
 ## Creating a custom codespace configuration