impl: Fix DevContainer on ARM

[lehors]

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

[netlify]

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