Currently I am appending a string `str` to the documentation of a function `myfun` using

(put myfun 'function-documentation
       (concat
          (documentation myfun t)
           str)

Whilst the strategy works, this requires adding `str` after the function `myfun` has been defined.
Does there exist the possibility to add `str` directly inside the docstring of the function when I am
defining the function itself, avoiding the `(put` command mentioned earlier after the implementation
of the function myfun?