man: Document that apt might expect Packages.xz too

debian/changelog

@@ -138,6 +138,7 @@ dpkg (1.18.0) UNRELEASED; urgency=low
     - Clarify that dpkg-buildpackage -jN forces parallel builds, regardless of
       the packaging or upstream build systems supporting them. Closes: #780866
     - Remove unneeded update-alternatives references from options descriptions.
+    - Document that apt might expect Packages.xz too in dpkg-scanpackages(1).
   * Output message fixes and improvements:
     - Remove trailing newline from string literal in warning calls.
     - Say “execute” instead of “exec” in Dpkg::Changelog::Parse error message.

man/dpkg-scanpackages.1

@@ -47,6 +47,8 @@ of machines.
 If you want to access the generated Packages file with
 .B apt
 you will probably need to compress the file with
+.BR xz (1)
+(generating a Packages.xz file),
 .BR bzip2 (1)
 (generating a Packages.bz2 file) or
 .BR gzip (1)