The lm-sensors package comes with a number of files under the doc directory when it is unpacked, but none of this information is copied to the appropriate place (/usr/share/doc/lm-sensors-2.7.0-r1/ I assume) by the ebuild.
While I do know stuff about this package I can't maintain it any more because I don't have a 2.4 box to test on. Most likely just adding "dodoc doc/*" to the src_install function will fix the bug though. Sorry.
added in cvs