Reusing repo README for marketplace is restrictive; add an option #10485

Apologies if this is the wrong place for this...

The docs for the manifest file state:

Have a README.md Markdown file in your extension's root folder and we will include the contents in the body of the extension details (on the Marketplace).

I recently got some comments that the Readme for my extension on GitHub is not very good to tell people what the project. I could add this to the top of the README, but it's redundant on the marketplace (as is installation instructions, which currently appear twice because I have them in my readme).

It would be great to have the option of using a different file than the same readme that GitHub will show on a repo page. That way, the GitHub-displayed README.md could explain what the project is and how to install it, whereas the marketplace-displayed file could omit this stuff (people on the marketplace or inside Code already know it's an extension and how to install it).