Templates: Update autogenerated docs to include platforms detail #175

When templates were located in microsoft/vscode-dev-containers, the platforms variable was used for the auto-generated README files.

Example 👇

Looks like we did migrate the variable so that it could be utilized for auto-generated docs, however, it seems to have slipped though the gaps - I'll update devcontainers/action to utilize it. Wondering, Jacob Hummer (@jcbhmr) would that be helpful?

Originally posted by Samruddhi Khandale (@samruddhikhandale) in devcontainers/templates#145 (comment)