mention ncftpput in gnupload --help

[Karl Berry]

Bruce Korb pointed out that ncftpput is far from universal.
Maybe a patch like this?

--- /tmp/gnupload       2009-12-14 00:24:38.000000000 -0800
+++ /u/karl/bin/gnupload        2009-12-14 16:28:26.000000000 -0800
@@ -97,4 +97,9 @@
            -- foobar-0.9.91.tar.gz
 
+gnupload uses the ncftpput program to do the transfers; if you don't
+happen to have an ncftp package installed, the ncftpput-ftp script in
+the build-aux/ directory of the gnulib package
+(http://savannah.gnu.org/projects/gnulib) may serve as a replacement.
+
 Report bugs to <address@hidden>.
 Send patches to <address@hidden>."