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

Bug: b/375598322
Change-Id: I7b4262840d3df87dda0a63bf78639e9c43401cd1

README

diff --git a/README b/README
new file mode 100644
index 0000000..1372f28
--- /dev/null
+++ b/README
@@ -0,0 +1,4 @@
+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.
+