Add auto-reload example (#2166)

examples/auto-reload/README.md

@@ -0,0 +1,18 @@
+# auto-reload
+
+This example shows how you can set up a development environment for your axum
+service such that whenever the source code changes, the app is recompiled and
+restarted. It uses `listenfd` to be able to migrate connections from an old
+version of the app to a newly-compiled version.
+
+## Setup
+
+```sh
+cargo install cargo-watch systemfd
+```
+
+## Running
+
+```sh
+systemfd --no-pid -s http::3000 -- cargo watch -x run
+```