make.conf.5: restore SYNC documentation

The SYNC variable is deprecated, but it is still supported, for
backward compatibility with mirrorselect --rsync.
diff --git a/man/make.conf.5 b/man/make.conf.5
index 74f047b..ddacf56 100644
--- a/man/make.conf.5
+++ b/man/make.conf.5
@@ -966,6 +966,32 @@
 Defaults to ${PORTDIR}/rpm.
+\fBSYNC\fR = \fI[RSYNC]\fR
+Insert your preferred rsync mirror here.  This rsync server
+is used to sync the local portage tree when `emerge \-\-sync` is run.
+Note that the \fBSYNC\fR variable is now deprecated, and instead the
+sync\-type and sync\-uri attributes in repos.conf should be used. See
+\fBportage\fR(5) for more information.
+Defaults to rsync://\-portage
+.B Usage:
+.B Examples:
+Note: For the ssh:// scheme, key\-based authentication might be of interest.
 \fBUNINSTALL_IGNORE\fR = \fI[space delimited list of fnmatch patterns]\fR
 This variable prevents uninstallation of files that match
 specific \fBfnmatch\fR(3) patterns. In order to ignore file