As a minimum, nfp ought to recognize a -h/--help option that would make the user aware of the -e option. E.g.:
$ nfp -h
Usage: nfp [OPTIONS]
Run user-defined actions on new files in watched directories.
options:
-h, --help show this help message and exit
-e, --edit edit configuration file
-V, --version show version information and exit
nfp will use $VISUAL/$EDITOR to edit the configuration file.
Users literally have hundreds, if not thousands, of commands available (my /usr/bin currently holds 7_136 commands), and it is unrealistic to expect that the user will remember that nfp has an option named -e that will invoke an editor on the configuration file — especially because nfp will probably rarely be called once the user has told it which directories to watch.
As you can see, I have also suggested a -V/--version option. This will be handy for users, packagers, and bug-reporters alike. Once nfp has been installed, there is literally no way of knowing which version is currently installed.
For --version I have suggested the short form -V with a capital V. It is not an option that will be used frequestly, and by using a capital V keeps the shorthand -v open for a potential --verbose, or similar.