CRAN comments

Author: stla

cran-comments.md

@@ -1,3 +1,8 @@
+This is a resubmission. The CRAN team asked me to add the references. There is 
+only one reference and it is a PhD thesis, which has no DOI and cannot be found 
+on the web. So I just wrote the author name, the year, and the title.
+
+
 ## Test environments
 
 * Ubuntu 18.04, R 3.6.3