nixpkgs' post-installation fixup moves the pages to share/man.  Tell guilt-help so that it can find them.

diff --git a/guilt-help b/guilt-help
index 93442a3..b29e059 100755
--- a/guilt-help
+++ b/guilt-help
@@ -34,7 +34,7 @@ case $# in
 		;;
 esac
 
-MANDIR=`dirname $0`/../man
+MANDIR=`dirname $0`/../share/man
 MANDIR=`(cd "$MANDIR"; pwd)`
 exec man -M "$MANDIR" "$page"