meta-skeleton: update to satisfy yocto-check-layer tests

Added readme to satisfy the readme file test.
Updated busybox bbappend to satisfy the signature test.

[YOCTO #13612]

(From OE-Core rev: b2419bfaf28903d52dd88a3db7985c71e8ed814a)

Signed-off-by: Scott Weaver <weaverjs@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-skeleton/README.skeleton

@@ -0,0 +1,4 @@
+meta-skeleton
+=============
+
+The meta-skeleton layer contains example recipes and configuration files.

meta-skeleton/recipes-core/busybox/busybox_%.bbappend

@@ -2,11 +2,12 @@
 # mechanism as the linux-yocto kernel recipe.
 #
 # The entries here will override any entries in the base busybox recipe
+# when DISTRO = "mydistro" is defined in your conf/local.conf file.
 #
 # More details can be found in the Kernel Dev Manual
 # http://www.yoctoproject.org/docs/current/kernel-dev/kernel-dev.html#changing-the-configuration
 FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
 
-SRC_URI += " \
+SRC_URI_append_mydistro += " \
 	    file://no_rfkill.cfg \
            "