dpkg-source(1): indicate the recommended source formats

Until dpkg-source really produces new formats by default, it's
good to recommend using those formats and to inform our users
of the plan to switch.

This paragraph can be removed when dpkg-source produces new formats by
default.

man/dpkg-source.1

@@ -197,6 +197,11 @@ of the official Debian keyrings
 and \fI/usr/share/keyrings/debian-maintainers.gpg\fP).
 
 .SH SOURCE PACKAGE FORMATS
+If you don't know what source format you should use, you should probably
+pick either "3.0 (quilt)" or "3.0 (native)". They will become the default
+formats in the near future. See http://wiki.debian.org/Projects/DebSrc3.0
+for information on the deployment of those formats within Debian.
+
 .SS Format: 1.0
 A source package in this format consists either of a \fB.orig.tar.gz\fP
 associated to a \fB.diff.gz\fP or a single \fB.tar.gz\fP (in that case