for non-standard things in the check directory

Maintainer: ‘Yuchao Jiang <yuchaoj@email.unc.edu>’

No Authors@R field in DESCRIPTION.
Please add one, modifying
  Authors@R: c(person(given = "Yuchao",
                      family = "Jiang",
                      role = c("aut", "cre"),
                      email = "yuchaoj@email.unc.edu"),
               person(given = c("Nancy", "R."),
                      family = "Zhang",
                      role = "aut"))
as necessary.
Found the following files/directories:
  ‘MDA231_tree.pdf’
Maintainer: ‘Yuchao Jiang <yuchaoj@email.unc.edu>’

No Authors@R field in DESCRIPTION.
Please add one, modifying
  Authors@R: c(person(given = "Yuchao",
                      family = "Jiang",
                      role = c("aut", "cre"),
                      email = "yuchaoj@email.unc.edu"),
               person(given = c("Nancy", "R."),
                      family = "Zhang",
                      role = "aut"))
as necessary.
Found the following files/directories:
  ‘MDA231_tree.pdf’
Found the following files/directories:
  ‘MDA231_tree.pdf’
Found the following files/directories:
  ‘MDA231_tree.pdf’
Found the following files/directories:
  ‘MDA231_tree.pdf’
Found the following files/directories:
  ‘MDA231_tree.pdf’