minor readme changes

[dsweber2]

Checklist

Please:

• Make sure this PR is against "dev", not "main" (unless this is a release
  PR).
• Request a review from one of the current epidatr main reviewers:
  brookslogan, dshemetov, nmdefries, dsweber2.
• Makes sure to bump the version number in DESCRIPTION. Always increment
  the patch version number (the third number), unless you are making a
  release PR from dev to main, in which case increment the minor version
  number (the second number).
• Describe changes made in NEWS.md, making sure breaking changes
  (backwards-incompatible changes to the documented interface) are noted.
  Collect the changes under the next release number (e.g. if you are on
  1.7.2, then write your changes under the 1.8 heading).

Change explanations for reviewer

sorry for the spam. First this, then the merge to main. should be submitting to CRAN after that though

Magic GitHub syntax to mark associated Issue(s) as resolved when this is merged into the default branch

• Resolves #{issue number}

[nmdefries]

question: Looks like this link redirects to the old URL. Is there a benefit to doing it this way?

[dsweber2]

cran prefers this format, for whatever reason

[dsweber2]

Found the following (possibly) invalid URLs:
  URL: https://cran.r-project.org/web/packages/epidatr/index.html
    From: README.md
    Status: 200
    Message: OK
    CRAN URL not in canonical form
  URL: https://www.cdc.gov/datastatistics/index.html
    From: README.md
    Status: 404
    Message: Not Found
  The canonical URL of the CRAN page for a package is 
    https://CRAN.R-project.org/package=pkgname

[dsweber2]

from the win_builder check

[dshemetov]

Huh, I guess it's kinda neat that it checks URLs for you.

[dshemetov]

This page says the canonical URL is

https://cran.r-project.org/package=package-name

not sure if win_builder will complain aobut that index.html in there

[dsweber2]

urlchecker::url_check() was satisfied, which gives a more obscure version of the win_builder result, so I think we're good. Thanks for the catch though