Rename intro.Rmd to NHSRplotthedots.Rmd

[francisbarton]

This will make the intro vignette appear in the pkgdown site navbar automatically as "Get started".

link

Otherwise I think we should sort the articles nav menu list so that 'intro' is at the top.

If we move it to the navbar as its own 'Get started' item, I think the current 3 other vignettes are probably OK in the order they're already in (alphabetical). Otherwise we could explictly reorder them in _pkgdown.yml with:

articles:
- title: Articles
  navbar: ~
  contents:
  - number-of-points-required
  - deviations
  - other-spc-tools

[francisbarton]

Closed by #228