One way that I was taught is via the HTDP "design contract". So in this case a "docstring" translates to defining the method contact (its inputs and outputs) and the purpose of the function (what the function does).

https://course.ccs.neu.edu/csg107/design-recipe.html is a random link that describes all the steps, with something like 2. being the one mentioned (I think, I'm not OP.)