Issue #855 - render readme as PR

[nikosbosse]

Description

This PR closes #855.

As discussed in the issue, this PR steals the render-readme yaml from the excellent epinowcast package.

Checklist

• [x] My PR is based on a package issue and I have explicitly linked it.
• [x] I have included the target issue or issues in the PR title as follows: issue-number: PR title
• [x] I have tested my changes locally.
• [x] I have added or updated unit tests where necessary.
• [x] I have updated the documentation if required.
• [x] I have built the package locally and run rebuilt docs using roxygen2.
• [x] My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• [x] I have added a news item linked to this PR.
• [x] I have reviewed CI checks for this PR and addressed them as far as I am able.

[sbfnk]

This will also add allcontributors, do you want that? See https://github.com/epinowcast/epinowcast?tab=readme-ov-file#contributors

If yes then I think you'll have to add an empty ## Contributors section to the end of the README.Rmd to activate it.

[nikosbosse]

Oh, right! I didn't intentionally want it, but now that it's there maybe we should start actively wanting it?

[sbfnk]

I think it's a nice thing to have.

[nikosbosse]

Added a ## Contributors at the end of the Readme.Rmd file