Release envsetup 3.0.0

[nicholas-masel]

Prepare for release:

• git pull
• Polish NEWS
• usethis::use_github_links()
• urlchecker::url_check()
• devtools::build_readme()
• devtools::check(remote = TRUE, manual = TRUE)
• devtools::check_win_devel()
• Update cran-comments.md
• git push

Submit to CRAN:

• devtools::submit_cran()
• Approve email

Wait for CRAN...

• Accepted 🎉
• usethis::use_github_release()
• usethis::use_dev_version(push = TRUE)