site-amd64-hw: Add README

BUG=None
TEST=None
RELEASE_NOTE=None

Change-Id: I896b12ec3a1052be3799a368bb88e46bd3233164
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/8820
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Saied Kazemi <saied@google.com>
Reviewed-by: Ismael Aleman <ialeman@google.com>
diff --git a/overlay-site-amd64-hw/README.md b/overlay-site-amd64-hw/README.md
new file mode 100644
index 0000000..4a2467d
--- /dev/null
+++ b/overlay-site-amd64-hw/README.md
@@ -0,0 +1,4 @@
+The site-amd64-hw board targets specific bare metal hardware and is entirely
+owned by the SITE appliance team. See go/edgeappliance for more details.
+
+Contact: site-appliance-os@google.com