chore: rename middleware dirs

middleware/request-extensions/README.md

@@ -0,0 +1,17 @@
+# Middleware: Add/Retrieve Request-Local Data
+
+This example showcases a middleware that adds and retrieves request-local data. See also the [middleware guide](https://actix.rs/docs/middleware).
+
+## Usage
+
+```sh
+cd middleware/request-extensions
+cargo run
+```
+
+Look in `src/add_msg.rs` to see how it works.
+
+## Routes
+
+- [GET /on](http://localhost:8080/on) - `200 OK` with "hello from middleware" body and console log showing the request passed through the middleware
+- [GET /off](http://localhost:8080/off) - `500 Internal Server Error` with "no message found" body and console log showing the request passed through the middleware