RFR: add README.md [v2]

[Andrei Rybak]

> 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

Andrei Rybak has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains one additional commit since the last revision:

  add README.md
  
  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
  rendered 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

-------------

Changes:
  - all: https://git.openjdk.org/duke/pull/2/files
  - new: https://git.openjdk.org/duke/pull/2/files/1d68763c..108669ce

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=duke&pr=2&range=01
 - incr: https://webrevs.openjdk.org/?repo=duke&pr=2&range=00-01

  Stats: 5 lines in 5 files changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/duke/pull/2.diff
  Fetch: git fetch https://git.openjdk.org/duke.git pull/2/head:pull/2

PR: https://git.openjdk.org/duke/pull/2