add firmware upgrade

Signed-off-by: Michel-FK <michel.stempin@funkey-project.com>

docs/tutorials/software/update.md

@@ -1,3 +1,28 @@
+A firmware upgrade can be performed simply over USB without opening the
+**FunKey S** console.
+
+Get the latest "**_FunKey-rootfs-x.y.z.fwu_**" firmware update file
+directly from [here][1] or from the bottom of the latest release page
+in the "assets" section:
+
+https://github.com/FunKey-Project/FunKey-OS/releases/latest
+
+![Github Release](/assets/images/Github_Release.png)
+
+| **Display**                                           | **Action**                                                                                                              |
+|:-----------------------------------------------------:|:------------------------------------------------------------------------------------------------------------------------|
+| ![RetroFE](/assets/images/Connection_PC.png)          | Connect the **FunKey S** to your computer using the provided micro USB cable, then open it to turn it on                |
+| ![RetroFE](/assets/images/RetroFE.png)                | At the launcher's main screen (example here with RetroFE), press the **MENU** key                                       |
+| ![RetroFE](/assets/images/Mount_USB.png)              | Press the **UP**/**DOWN** keys until you see "**MOUNT USB**"                                                            |
+| ![RetroFE](/assets/images/Mount_USB_are_you_sure.png) | Press the **A** key twice to confirm                                                                                    |
+| ![RetroFE](/assets/images/Eject_USB.png)              | "**EJECT USB**" is now displayed instead, now go to your host computer and open a File Explorer window                  |
+| ![RetroFE](/assets/images/USB_Drive.png)              | You should see the FunKey S appear as an USB drive on your computer in the File Explorer (example here with Windows 10) |
+| ![RetroFE](/assets/images/USB_Drag_Drop.png)          | Drag & drop the _FunKey-roots-2.0.0.fwu_ file you just downloaded at the root of this USB drive on your computer        |
+| ![RetroFE](/assets/images/Eject_Drive.png)            | Eject cleanly the USB drive from your computer                                                                          |
+| ![RetroFE](/assets/images/Eject_USB_are_you_sure.png) | Back on the **FunKey S**, at the "**EJECT USB**" menu entry, press the "**A**" key twice to confirm                     |
+| ![RetroFE](/assets/images/Updating.png)               | The **FunKey S** will then reboot and perform the upgrade                                                               |
+
+[1]: https://github.com/FunKey-Project/FunKey-OS/releases/download/FunKey-OS-2.0.0/FunKey-rootfs-2.0.0.fwu
 
 --8<--
 includes/glossary.md

mkdocs.yml

@@ -98,6 +98,7 @@ markdown_extensions:
   - pymdownx.tabbed
   - pymdownx.tasklist:
       custom_checkbox: true
+      clickable_checkbox: true
   - pymdownx.tilde
 
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