Docs for templates apply command (#388)

* templates apply command

* Update apply.md

docs/templates/apply.md

@@ -0,0 +1,55 @@
+# Applying a Dev Container Template to a folder with the CLI
+
+## Summary
+
+The CLI can be used to apply (download) a [Dev Container Template](https://containers.dev/implementors/templates) to a provided folder.  
+
+Templates can be published via the `templates publish` command - see [the template-starter repo](https://github.com/devcontainers/template-starter) for more information.
+
+To see all the available options, run `devcontainers templates apply --help`.
+
+## Example
+
+To apply the [debian template](https://github.com/devcontainers/templates/tree/main/src/debian) to a local folder with the CLI, execute the following steps.
+
+```
+[/tmp]$ mkdir my-project
+
+[/tmp]$ devcontainer templates apply \
+                 -t 'ghcr.io/devcontainers/templates/debian' \
+                 -a '{"imageVariant": "buster"}' \
+                 -w ./my-project
+
+[0 ms] @devcontainers/cli 0.28.0. Node.js v19.3.0. darwin 21.6.0 arm64.
+{"files":["./.devcontainer/devcontainer.json"]}
+
+[/tmp]$ tree -a my-project
+
+my-project
+└── .devcontainer
+    └── devcontainer.json
+
+1 directory, 1 file
+
+[/tmp]$ cat my-project/.devcontainer/devcontainer.json
+
+{
+	"name": "Debian",
+	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+	"image": "mcr.microsoft.com/devcontainers/base:buster"
+
+	// Features to add to the dev container. More info: https://containers.dev/features.
+	// "features": {},
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Configure tool-specific properties.
+	// "customizations": {},
+
+	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+	// "remoteUser": "root"
+}
+```
+
+Any omitted `templateArgs` will be substituted with the `default` value declared in the Template's `devcontainer-template.json`.