Add README with details about the status of support for this app

Bug: b/375598322
Change-Id: Ia83c8e4c028b33ff040409c748419146f5bfa290

README

diff --git a/README b/README
new file mode 100644
index 0000000..ff1d3d0
--- /dev/null
+++ b/README
@@ -0,0 +1,3 @@
+This app is not actively supported and the source is only available as a
+reference. This project will be removed from the source manifest sometime in
+the future.
\ No newline at end of file