If the whatis database does not exist run "makewhatis" as root, or if you don't have root access run "makewhatis -o whatis" to make your own personal copy. You also need the games distribution files installed.
Ok let's make fortunes...
To make the whole whatis database into a fortune file:
$ cat /usr/share/man/whatis | sed 's/$/\
\%/g' > whatis-fortune
$ /usr/games/strfile whatis-fortune whatis-fortune.dat
[Note that the sed command is split over two lines, type it exactly as shown.]
To make just one man section into a fortune file, section 1 in this example:
$ cat /usr/share/man/whatis | egrep "^.+\(1\) +- " | sed 's/$/\
\%/g' > whatis1-fortune
$ /usr/games/strfile whatis1-fortune whatis1-fortune.dat
Naturally substitute 1 with any man section number to make a different fortune file.
Test it with "fortune whatis1-fortune".
If everything is happy you can put it in your .profile (under the freebsd-tips fortune line of course) with the full path to the fortune files if you didn't put them in /usr/share/games/fortune.