The README is in /usr/share/doc/command-not-found/README and says:-
To use it please add the following line to your .bashrc file: . /etc/bash_command_not_found
(actually it says add ". /etc/bash_command_nof_found" but that has already been reported as a bug:- https://bugs.launchpad.net/ubuntu/+source/command-not-found/+bug/94088)
You will need to start a new terminal or logout and login again for that change to take effect I suspect.
More information about formatting options
There is a readme..
The README is in /usr/share/doc/command-not-found/README and says:-
(actually it says add ". /etc/bash_command_nof_found" but that has already been reported as a bug:- https://bugs.launchpad.net/ubuntu/+source/command-not-found/+bug/94088)
You will need to start a new terminal or logout and login again for that change to take effect I suspect.