This function looks for files in the R/ and src/ folders and gives some stats. If there is no R/ folder directly accessible from the working directory, there will be no stats displayed.
Why this function? Well, it's just some goodies for package developers trying to be user-friendly!
The number of documentation lines (and number of words) corresponds to the number of non-empty roxygen documentation lines. So if you don't document your code with roxygen, well, this stat won't prompt.
Code lines correspond to non-commented, non-empty lines (by non empty: at least one letter must appear).
Comment lines are non-empty comments.