package: include package/skeleton/Config.in

This was missing from the patch introducing the skeleton package. It
was working fine, except that the skeleton package was not in the
global variable PACKAGES.

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

package/Config.in

@@ -1,5 +1,6 @@
 menu "Target packages"
 
+	source "package/skeleton/Config.in"
 	source "package/busybox/Config.in"
 
 menu "Audio and video applications"