Upkeep for openairmaps (2023)

[jack-davison]

• usethis::use_github_links()
• usethis::use_tidy_description()
• Align the names of R/ files and test/ files for workflow happiness. The docs for usethis::use_r() include a helpful script. usethis::rename_files() may be be useful.
• Consider changing default branch from master to main
• Remove description of test environments from cran-comments.md.
  See usethis::use_cran_comments().
• Add alt-text to pictures, plots, etc; see https://posit.co/blog/knitr-fig-alt/ for examples

Set up or update GitHub Actions.
Updating workflows to the latest version will often fix troublesome actions:

• usethis::use_github_action('check-standard')
• usethis::use_github_action('pkgdown')
• usethis::use_github_action('test-coverage')

^{Created on 2023-08-02 with usethis::use_upkeep_issue(), using usethis v2.2.1}