docs: add README and LICENSE to Rust client and mux crates

mux/rust/README.md

@@ -0,0 +1,28 @@
+# DongLoRa Mux (Rust)
+
+USB multiplexer daemon — lets multiple applications share one DongLoRa
+dongle simultaneously.
+
+## What It Does
+
+- Owns the USB serial connection exclusively
+- Exposes a Unix domain socket (and optional TCP) speaking the same
+  COBS-framed protocol
+- RxPacket frames broadcast to all connected clients
+- StartRx/StopRx reference-counted across clients
+- SetConfig locked once set (single client can change freely)
+- Automatic dongle reconnect on hot-plug
+- No panics — enforced by clippy deny lints
+
+## Running
+
+```sh
+just run                                    # start the mux daemon
+just verbose                                # start with verbose logging
+just run -- --tcp 5741 --port /dev/ttyACM0  # with options
+```
+
+## Depends On
+
+- [clients/rust](../../clients/rust/) — the `donglora-client` library
+  (protocol types, COBS framing, device discovery)