Move Iris to its standalone repository

docs/RUST.md

@@ -1,7 +1,8 @@
 # Rust app and Iris
 
 The production app is one Rust crate under `app/`, with shared Android and
-desktop UI drawn by the in-tree `iris` framework. This document keeps the
+desktop UI drawn by the `iris` framework pinned under `iris/` as a submodule.
+This document keeps the
 open work and measured constraints that are expensive to rediscover.
 
 ## Boundaries