Add Garrison README

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

Change-Id: Ib3040500ed8b634b1fb0f5ce1b3156f7885d49aa
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/meta-openbmc-machines/meta-openpower/meta-ibm/meta-garrison/README.md b/meta-openbmc-machines/meta-openpower/meta-ibm/meta-garrison/README.md
new file mode 100644
index 0000000..cb0abea
--- /dev/null
+++ b/meta-openbmc-machines/meta-openpower/meta-ibm/meta-garrison/README.md
@@ -0,0 +1,6 @@
+Garrison
+================
+
+This is the Garrison machine layer.
+
+Garrison is no longer a supported machine.