Presence of inst/doc triggering warning

[shntnu]

Before submitting, ensure that inst/doc is empty. Doing so removes this warning. Update cran-comments.md now that this is fixed

* checking files in 'vignettes' ... WARNING
 Files in the 'vignettes' directory newer than all files in 'inst/doc': 
'cytominer-pipeline.Rmd'

[shntnu]

See https://stackoverflow.com/a/40184732/1094109 (following those instructions, i.e., delete inst/doc, worked)
Also read r-lib/devtools#1348

[shntnu]

#86