feat(demo): MicroPython REPL works!

update README with relevant instructions

README.md

@@ -1,14 +1,25 @@
 # rp2040js
 
-A Raspberry Pi Pico Emulator (WiP). It (almost) blinks!
+A Raspberry Pi Pico Emulator (WiP). It blinks, runs Arduino code, and even the MicroPython REPL!
 
-## Enjoy the wonders
+## Run the demo project
+
+You'd need to get `hello_uart.hex` by building it from the [pico-examples repo](https://github.com/raspberrypi/pico-examples/tree/master/uart/hello_uart), then copy it to the rp2040js root directory and run:
 
 ```
 npm install
 npm start
 ```
 
+To run the micropython demo, first download [rp2040-micropython-uart-47e6c52f0c.hex](https://raw.githubusercontent.com/wokwi/firmware-assets/gh-pages/rp2040-micropython-uart-47e6c52f0c.hex), rename it to `micropython.hex` and place it in the rp2040js root directory, then run:
+
+```
+npm install
+npm run start:micropython
+```
+
+and enjoy the MicroPython REPL! Quit the REPL with Ctrl+D.
+
 ## Learn more
 
 - [Live-coding stream playlist](https://www.youtube.com/playlist?list=PLLomdjsHtJTxT-vdJHwa3z62dFXZnzYBm)

demo/emulator-run.ts

@@ -15,7 +15,7 @@ const gdbServer = new GDBTCPServer(mcu, 3333);
 console.log(`RP2040 GDB Server ready! Listening on port ${gdbServer.port}`);
 
 mcu.uart[0].onByte = (value) => {
-  console.log('UART sent: ', String.fromCharCode(value));
+  process.stdout.write(new Uint8Array([value]));
 };
 
 mcu.PC = 0x10000000;

demo/micropython-run.ts

@@ -18,6 +18,15 @@ console.log(`RP2040 GDB Server ready! Listening on port ${gdbServer.port}`);
 mcu.uart[0].onByte = (value) => {
   process.stdout.write(new Uint8Array([value]));
 };
+process.stdin.setRawMode(true);
+process.stdin.on('data', (chunk) => {
+  if (chunk[0] === 4) {
+    process.exit(0);
+  }
+  for (const byte of chunk) {
+    mcu.uart[0].feedByte(byte);
+  }
+});
 
 mcu.PC = 0x10000000;
 mcu.execute();