binder: rust: Document DeathRecipient drop effects

Bug: 181953084
Test: None
Change-Id: I49911f5ebdcf0941f47683e554a0068e0fcda095
diff --git a/libs/binder/rust/src/proxy.rs b/libs/binder/rust/src/proxy.rs
index 126b202..862fc2a 100644
--- a/libs/binder/rust/src/proxy.rs
+++ b/libs/binder/rust/src/proxy.rs
@@ -561,6 +561,9 @@
 /// The cookie in this struct represents an Arc<F> for the owned callback.
 /// This struct owns a ref-count of it, and so does every binder that we
 /// have been linked with.
+///
+/// Dropping the `DeathRecipient` will `unlink_to_death` any binders it is
+/// currently linked to.
 #[repr(C)]
 pub struct DeathRecipient {
     recipient: *mut sys::AIBinder_DeathRecipient,