I have a package for interacting with GRASS GIS processes, available on MELPA. The rate of development and number of users are both quite low, so there's no need for a mailing list or any formal communications with my users.
However, I've just introduced some changes to the configuration options that will require some attention from my users - how can I communicate this to them, given that for most of them all they will see is the updated package coming in from MELPA? Is there a way to pass a message on to users that they will see the first time they run code after a certain change has been made? What is best-practice in this regard?