Perform update and raise notice in Postgres Function

I'm trying to add a notice (or something similar) to a function that is executed on update by a trigger in PostgreSQL 9.6 db. I want to let the user who edited the table that something happened. I don't know is "NOTICE" is the proper RAISE (Why not "INFO"?). The central question is: **how I can add the raise notice argument after the update?**