lftp: indicate why autoreconf is needed

We no longer have any patch touching configure.ac/Makefile.am, so one
might wonder why we're autoreconfiguring the package. The reason is
that our libtool patch doesn't apply on the code provided by the lftp
tarball.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/lftp/lftp.mk

@@ -9,6 +9,7 @@ LFTP_SOURCE = lftp-$(LFTP_VERSION).tar.xz
 LFTP_SITE = http://lftp.yar.ru/ftp
 LFTP_LICENSE = GPLv3+
 LFTP_LICENSE_FILES = COPYING
+# Needed so that our libtool patch applies properly
 LFTP_AUTORECONF = YES
 LFTP_DEPENDENCIES = readline zlib host-pkgconf