Provide more context on tool-specific properties

[alfredodeza]

Currently most (all?) templates provide an entry for customizations similar to:

	// Configure tool-specific properties.
	// "customizations": {},

But new users to Codespaces and devcontainers.json specifically, do not understand how to add an extension or how that looks like. It would be useful to have either a link to documentation or a sample ID for a VSCode extension that could be used (or both).

The feature of right-clicking an extension and selecting "add to devcontainer.json" is incredibly useful but hardly used because there isn't awareness.

This issue in particular is brought forward based on feedback from students while learning to use Devcontainers for the first time.

[bamurtaugh]

Thanks for opening this issue and sharing this feedback, @alfredodeza!

Please feel free to open a PR updating the comment for even just one of the templates, and we could discuss and iterate from there.