impl: Fix DevContainer on ARM (#1573)

Netlify 23.15.1 on ARM fails to install a working version of deno, so
launching netlify then fails. This installs the latest version of deno
which works on ARM.

Also expand a bit the documentation on using the DevContainer.

FYI, here is the error (which I did report) on running `netlify dev -c
'bundle exec jekyll serve --livereload --incremental'`:
```
✖ Setting up the Edge Functions environment. This may take a couple of minutes.
 ›   Error: Netlify CLI has terminated unexpectedly
This is a problem with the Netlify CLI, not with your application.
If you recently updated the CLI, consider reverting to an older version by running:

npm install -g netlify-cli@VERSION

You can use any version from https://ntl.fyi/cli-versions.

Please report this problem at https://ntl.fyi/cli-error including the error details below.

Error: Failed to set up Deno for Edge Functions.
Error: Command failed with exit code 255: /root/.config/netlify/deno-cli/deno --version
qemu-x86_64-static: Could not open '/lib64/ld-linux-x86-64.so.2': No such file or directory
Downloaded to: /root/.config/netlify/deno-cli/deno
Platform: linux/arm64

```

---------

Signed-off-by: Arnaud J Le Hors <lehors@us.ibm.com>

Author: lehors

.devcontainer/post-create.sh

@@ -14,5 +14,10 @@ bundle install
 # Install the Netlify CLI globally using npm
 npm install -g netlify-cli
 
+# Netlify 23.15.1 on ARM fails to install a working version of deno,
+# so install the latest one directly.
+# Note: this should not be necessary once netlify is fixed
+npm install -g deno
+
 # Return to the previous directory
 cd ..

CONTRIBUTING.md

@@ -78,6 +78,13 @@ If you prefer to work locally, you can use VS Code with the DevContainers extens
 
 VS Code will build the container and configure the development environment automatically. **The initial setup may take a few minutes as the container is built.**
 
+Once done, you can open a Terminal and launch the development server in the DevContainer with the following command:
+
+```shell
+cd docs
+netlify dev -c 'bundle exec jekyll serve --livereload --incremental'
+```
+
 ### Deploying the site locally
 
 SLSA.dev is hosted on [Netlify](https://www.netlify.com/), and you can run a local development server using the Netlify CLI.