Crack Password – How To Define Rules For Jack The Ripper

I'm very new to ripping the ripper, and I wonder how to crack a txt file with special rules. The password of my txt file is 123 and in single-crack mode it takes a lot of time to crack this simple password.
I was looking for

maxlen

in that

john.conf

File and replaces the maximum length with 3 (in [Incremental:Digits]).
If I save the file and try to crack the password again, it still does not run much faster.
Can someone explain to me how to crack such simple passwords in a reasonable amount of time?
I crack the password by typing

    sudo john --incremental: Digits example.txt

in the bash
I also work with Linux Ubuntu.
Thanks for your help.