some doc updates

add a 'distrib' target to the top level Makefile so that the
distribution doc/*.txt files can be created via 'make distrib'
from the top directory.  It utilizes the existing 'distrib'
target in the doc/Makefile.

Have hints/linux.370 specify the correct directory for Linux
man pages of /usr/share/man/man6, so that 'sudo make manpages'
works on that platform,

sys/unix/Makefile.doc

@@ -81,7 +81,7 @@ $(MAKEDEFS)	: ../util/makedefs.c ../include/config.h ../src/mdlib.c \
 	( cd ../util ; make makedefs )
 
 GAME	= nethack
-MANDIR	= /usr/man/man6
+MANDIR	?= /usr/man/man6
 MANEXT	= 6
 
 # manual installation for most BSD-style systems

sys/unix/Makefile.top

@@ -173,6 +173,9 @@ Guidebook.pdf:
 manpages:
 	( cd doc ; $(MAKE) manpages )
 
+distrib:
+	( cd doc ; $(MAKE) distrib )
+
 data: $(GAME)
 	( cd dat ; $(MAKE) data )
 

sys/unix/hints/linux.370

@@ -350,7 +350,9 @@ CHGRP=true
 VARDIRPERM = 0755
 VARFILEPERM = 0600
 GAMEPERM = 0755
-
+#
+# manpages directory
+MANDIR=/usr/share/man/man6
 #
 #-INCLUDE cross-pre.370
 #