Add some Package URL syntax

doc/development/design/index.mdwn

@@ -73,8 +73,8 @@
         + Not great... this is specific to project-renard. It downloads the
           test data and sets an environment variable.
     * Each platform has a `_install` method (task: Install).
-        + Debian + apt: Install `xvfb xauth`.
-            + `xauth` is only needed for the `xvfb-run` script. `xvfb-run`
+        + Debian + apt: Install `pkg:deb/debian/xvfb`, `pkg:deb/debian/xauth`.
+            + `pkg:deb/debian/xauth` is only needed for the `xvfb-run` script. `xvfb-run`
               seems to be distribution-specific
               (i.e., the script is not provided by the upstream `xorg-server`
               package but is packaged by some Linux distributions such as