Package check result: NOTE

Check: CRAN incoming feasibility, Result: NOTE
  Maintainer: ‘Chris Bielow <chris.bielow@bsc.fu-berlin.de>’
  
  Found the following (possibly) invalid URLs:
    URL: http://htmlpreview.github.io/?https://github.com/cbielow/PTXQC/blob/master/docs/index.html
      From: README.md
      Status: 503
      Message: Service Unavailable

No changes to worse in reverse depends.