Closes #242: Added link for Preview SDTM vignette in README.md [create website]

[Lina2689]

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[github-actions]

Package	Line Rate	Health
pharmaversesdtm	0%	❌
Summary	0% (0 / 41)	❌

[github-actions]

The website/documentation is availables at https://pharmaverse.github.io/pharmaversesdtm/242-documentation-add-link-for-preview-sdtm-vignette-in-readmemd/dev.