move explainer

Author: nikomatsakis

SUMMARY.md

@@ -29,6 +29,10 @@
     - [Bound items](./evaluation/design/bound_items.md)
     - [With clauses](./evaluation/design/with_clauses.md)
 - [📚 Explainer](./explainer.md)
+  - [Phase 1](./explainer/phase_1.md)
+  - [Phase 1 narrative](./explainer/phase_1_narrative.md)
+  - [Phase 2](./explainer/phase_2.md)
+  - [Phase 3](./explainer/phase_3.md)
 - [✨ RFC](./RFC.md)
   - [Static async fn in traits](./RFC/static_async_fn_in_traits.md)
 - [💬 Design discussions](./design-discussions/README.md)

explainer.md

@@ -2,4 +2,16 @@
 
 > The "explainer" is "end-user readable" documentation that explains how to use the feature being deveoped by this initiative.
 > If you want to experiment with the feature, you've come to the right place.
-> Until the feature enters "feature complete" form, the explainer should be considered a work-in-progress.
+> Until the feature enters "feature complete" form, the explainer should be considered a work-in-progress.
+
+Async functions in traits are expected to "roll out" in stages, so we actually have several explainers, one for each phase:
+
+* [Phase 1](./explainer/phase_1.md): Stable compiler supports async fn in traits, dynamic dispatch supported via [`dyner`] crate
+    * [Narrative form]()
+* Phase 2: Build on async fn in traits support:
+    * async closures
+    * async drop
+    * `AsyncRead`, `AsyncWrite`, `Stream` (the [portability initiative] is driving the design of these traits)
+* Phase 3: Circle back to dynamic dispatch, incorporating the lessons we've learned from the `dyner` crate
+
+[`dyner`]: https://github.com/nikomatsakis/dyner