no man page for pnmtopng

[Ted Unangst]

carbolite:~> pnmtopng -?
pnmtopng: Use 'man pnmtopng' for help.
carbolite:~> man pnmtopng
man: No entry for pnmtopng in the manual.

This feel vaguely familiar, but I can't remember why it is so.