Update tokio/src/runtime/task/mod.rs

Co-authored-by: Eliza Weisman <eliza@buoyant.io>

tokio/src/runtime/task/mod.rs

@@ -249,6 +249,12 @@ pub fn id() -> Id {
 /// This function is similar to  [`task::id()`](crate::runtime::task::id()), except
 /// that it returns `None` rather than panicking if called outside of a task 
 /// context.
+///
+/// **Note**: This is an [unstable API][unstable]. The public API of this type
+/// may break in 1.x releases. See [the documentation on unstable
+/// features][unstable] for details.
+///
+/// [task ID]: crate::task::Id
 #[cfg_attr(not(tokio_unstable), allow(unreachable_pub))]
 #[track_caller]
 pub fn try_id() -> Option<Id> {