The license information for R packages is specified in the DESCRIPTION file for a "standard" open source license--this project is licensed under MIT, as specified there. For the MIT license, you need an additional LICENSE file that just states the copyright holder and year, which is exactly what the author has provided.
Ideally though, for the sake of people looking at the GitHub repo, I think they ought to do the following:
1. Rename LICENSE file to COPYRIGHT and change the line
License: MIT + file LICENSE
in the DESCRIPTION file to
License: MIT + file COPYRIGHT
2. Put a full copy of the MIT license with both copyright notice and MIT license text in a file named LICENSE. This allows GitHub to recognize the license and tag the repo accordingly. Additionally it allows people to see the license by looking at that file regardless of language instead of having to know language specific conventions.
3. Optionally, delete the LICENSE.md file unless it is useful elsewhere.
Assuming of course that having the license text and not just copyright notice in LICENSE won’t interfere with R packaging tools once the DESCRIPTION file specifies to use file COPYRIGHT instead.
I think that is good advice but it’s not a great fit for R packages due to the requirements that CRAN has for package submission. I’ve wrapped up my recommended practices in usethis::use_mit_license().
