Fix doc

[chainsawriot]

So that it prevents the WARN generated by the devel version of R

  Found the following Rd file(s) with Rd \link{} targets missing package
  anchors:
    readtext.Rd: fread
  Please provide package anchors for all Rd \link{} targets not in the
  package itself and the base packages.

[kbenoit]

Thanks!