Add docs for devcontainer templates publish (#410)

* Add docs for `devcontainer templates publish`

ref: microsoft/vscode-dev-containers#1238

* Update publish.md

* Update publish.md

* Update docs/templates/publish.md

Co-authored-by: Samruddhi Khandale <[email protected]>

* Update publish.md

---------

Co-authored-by: Samruddhi Khandale <[email protected]>

Author: joshspicer

docs/templates/publish.md

@@ -0,0 +1,65 @@
+# Publishing Dev Container Templates
+
+> NOTE: You may want to first check out our [templates-starter](https://github.com/devcontainers/template-starter), which includes an example [actions workflow](https://github.com/devcontainers/action) for publishing directly out of your GitHub repo!
+
+## Summary
+
+The CLI can be used to publish [Dev Container Template](https://containers.dev/implementors/templates/) artifacts to an OCI registry (that supports the [artifacts specification](https://oras.land/implementors/)).
+
+To see all the available options, run `devcontainers templates publish --help`.
+
+## Example
+
+Given a directory that is organized according to the [Templates distribution specification](https://containers.dev/implementors/templates-distribution/) - for example:
+
+```
+├── src
+│   ├── color
+│   │   ├── devcontainer-template.json
+│   │   └──| .devcontainer
+│   │      └── devcontainer.json
+│   ├── hello
+│   │   ├── devcontainer-template.json
+│   │   └──| .devcontainer
+│   │      ├── devcontainer.json
+│   │      └── Dockerfile
+|   ├── ...
+│   │   ├── devcontainer-template.json
+│   │   └──| .devcontainer
+│   │      └── devcontainer.json
+├── test
+│   ├── color
+│   │   └── test.sh
+│   ├── hello
+│   │   └── test.sh
+│   └──test-utils
+│      └── test-utils.sh
+...
+```
+
+The following command will publish each Template above (`color,hello`) to the registry `ghcr.io` with the following namespace (prefix) `devcontainers/templates`.
+
+```
+[/tmp]$  GITHUB_TOKEN="$CR_PAT" devcontainer templates publish -r ghcr.io -n devcontainers/templates ./src
+```
+
+To later apply a published Template (in the example below, the `color` template) with the CLI, the following [apply](../apply) command would be used:
+
+```
+[/tmp]$  devcontainer templates apply \
+                 -t 'ghcr.io/devcontainers/templates/color' \
+                 -a '{"favorite": "red"}'
+```
+
+### Authentication Methods
+
+> NOTE: OS-specific docker credential helpers (Docker Desktop credential helper) are not currently recognized by the CLI.  
+
+- Adding a $HOME/.docker/config.json with your credentials following [this commonly defined format](https://www.systutorials.com/docs/linux/man/5-docker-config-json/).
+   - Your `docker login` command may write this file for you depending on your operating system.
+- Using our custom env variable DEVCONTAINERS_OCI_AUTH
+    - eg: `DEVCONTAINERS_OCI_AUTH=service1|user1|token1,service2|user2|token2`
+    
+For publishing to `ghcr.io`
+- Using the `devcontainers/action` GitHub action to handle the `GITHUB_TOKEN` credential for you.
+- Providing a GITHUB_TOKEN with permission to `write:packages`.