RFR: add README.md

[Andrei Rybak]

On Sun, 13 Aug 2023 11:15:35 GMT, Andrei Rybak <duke at openjdk.org> wrote:

> Add a README.md file in Markdown format with a link to the project on openjdk.org and with a banner of welcome.jpg file.  README.md is nicely formatted by repository browsers like [GitHub][1] on the landing page of the repository.
>     
> [1]: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-readmes
> 
> ----
> 
> How the file is rendered can be seen on GitHub: https://github.com/openjdk/duke/blob/1d68763c12afac7f5a3b15f02937afe567d0256a/README.md

@irisclark and @jeffatsun, could you please consider reviewing and sponsoring this pull request? Asking, since I noticed some recent activity in the repository.

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PR Comment: https://git.openjdk.org/duke/pull/2#issuecomment-3099762048