Proposal: r-lib/package-development-workflow skill

[davidrsch]

Following up on PR #13 and your recommendation to discuss skill boundaries first!

I'd like to propose a foundational R package skill: r-lib/package-development-workflow.

This skill establishes the modern "edit → load → test-drive → document → check" workflow for R package development using usethis and devtools. It would act as an anchor skill for AI agents interacting with R packages.

Key contexts this skill would enforce:

• Strongly preferring devtools::load_all() instead of library() or source().
• The playbook for usethis scaffolding (use_r(), use_package(), use_test(), etc.).
• Explaining the constraints of R CMD check and why warnings/notes matter.
• Establishing RStudio project structure and path discipline (here::here() vs relative paths).

Let me know if you think this boundary makes sense for the repo, or if it should be scoped differently! If it looks good, I'll open a small, isolated PR with just this skill so it's easy to review.