Development progress

- many small fixes
- add hello-world
- fix source code

src/hello-world/02.02.WINDOWS.md

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+# Windows tooling
+
+Before plugging the Serial module, run the following command on the terminal:
+
+``` console
+$ mode
+```
+
+It will print a list of devices that are connected to your laptop. The ones that start with `COM` in
+their names are serial devices. This is the kind of device we'll be working with. Take note of all
+the `COM` *ports* `mode` outputs *before* plugging the serial module.
+
+Now, plug the Serial module and run the `mode` command again. You should see a new `COM` port appear
+on the list. That's the COM port assigned to the serial module.
+
+Now launch `putty`. A GUI will pop out.
+
+<p align="center">
+<img title="PuTTY settings" src="assets/putty-settings.png">
+</p>
+
+On the starter screen, which should have the "Session" category open, pick "Serial" as the
+"Connection type". On the "Serial line" field enter the `COM` device you got on the previous step,
+for example `COM3`.
+
+Next, pick the "Connection/Serial" category from the menu on the left. On this new view, make sure
+that the serial port is configured as follows:
+
+- "Speed (baud)": 115200
+- "Data bits": 8
+- "Stop bits": 1
+- "Parity": None
+- "Flow control": None
+
+Finally, click the Open button. A console will show up now:
+
+<p align="center">
+<img title="PuTTY console" src="assets/putty-console.png">
+</p>
+
+If you type on this console, the TX (red) LED on the Serial module should blink. Each key stroke
+should make the LED blink once. Note that the console won't echo back what you type so the screen
+will remain blank.