Package check result: NOTE

Check: CRAN incoming feasibility, Result: NOTE
  Maintainer: ‘Yichen Wang <wayichen@umich.edu>’
  
  Suggests or Enhances not in mainstream repositories:
    DoubletFinder, RcppPlanc
  Availability using Additional_repositories specification:
    DoubletFinder   yes   https://blaserlab.r-universe.dev
    RcppPlanc       yes   https://welch-lab.r-universe.dev
  
  Found the following (possibly) invalid URLs:
    URL: https://singlecell.broadinstitute.org/single_cell
      From: README.md
      Status: Error
      Message: server verification failed: certificate signer not trusted. (CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none)