Add Firestone README

Added a Firestone README with a line about Firestone no longer
being a supported machine. This can up updated in the future
if Firestone becomes supported again.

Change-Id: I9b845b56e57333323a119250a775a378d9a10955
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/meta-ibm/meta-firestone/README.md b/meta-ibm/meta-firestone/README.md
new file mode 100644
index 0000000..cc10d89
--- /dev/null
+++ b/meta-ibm/meta-firestone/README.md
@@ -0,0 +1,6 @@
+Firestone
+================
+
+This is the Firestone machine layer.
+
+Firestone is no longer a supported machine.