Copenhagen: Remind users to use ?function() when unsure about the use: example with ends_with()

[JoaodcPires]

For the section:

## ----skim_dose_cols-----------------------------------------------------------

drskim <- linelist %>% 
  # Select all columns with names that end in upper case 'D':
  select(ends_with("D", ignore.case = FALSE)) %>% 
  # Produce the skim summary table
  skimr::skim()

Add the following documentation:

## check the function ends_with()
?ends_with
## by default the function ignores upper or lower case inputs.
## If we would use the default ignore.case = T, the variable bread would also be selected

drskim <- linelist %>% 
  # Select all columns with names that end in upper case 'D':
  select(ends_with("D", ignore.case = FALSE)) %>% 
  # Produce the skim summary table
  skimr::skim()