doc: Add STM32 serial bootloader

doc/content/getting-started/programming-software/stm32-serial-bootloader/_index.md

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+---
+title: "STM32's Serial Bootloader"
+description: ""
+weight:
+distributions: null
+---
+
+If you don't have an ST-LINK V3 probe for programming the Generic Node Sensor Edition, you can program it through a **USB-to-UART TTL converter** (sometimes referred to as a serial converter). They are commonly available as breakout boards, such as the [SparkFun FTDI Basic Breakout - 3.3V](https://www.sparkfun.com/products/9873), for example.
+
+{{< note "Make sure to use an USB-to-UART  converter  board configured to 3.3v for both power output and I/O levels. If you have a 5V FTDI breakout board, check if it has a jumper that allows you to switch it to 3.3v." />}}
+
+Install drivers on your computer if they are not already installed. Follow the tutorials on the **SparkFun** website to learn how to install them on different operating systems:
+
+- Windows: https://learn.sparkfun.com/tutorials/how-to-install-ftdi-drivers/windows---in-depth
+- Mac: https://learn.sparkfun.com/tutorials/how-to-install-ftdi-drivers/mac
+- Linux: https://learn.sparkfun.com/tutorials/how-to-install-ftdi-drivers/linux
+
+Connect GNSE with the FTDI breakout using jumper wires as shown below:
+
+{{< figure src="gnse-ftdi.png" alt="" >}}
+
+Please refer to the table below for clarity:
+
+| GNSE   | FTDI |
+|--------|------|
+| TXD    | RXI  |
+| RXD    | TXO  |
+| VCC    | 3V3  |
+| GND    | GND  |
+
+Connect FTDI to the computer using miniUSB cable.
+
+Now, you need the `.bin` file of your project to flash onto the GNSE using [STM32CubeProgrammer]({{< ref "/getting-started/programming-software/st-examples/stcubeprog" >}}). This file can be generated during the build process with the [STM32CubeIDE]({{< ref "/getting-started/programming-software/st-examples/stcubeide" >}}). To configure the generation of a `.bin` file, right-click on the **project** and select **Properties** from the shortcut menu.
+
+In the **Properties** window, expand **C/C++ Build** and then select **Settings**. In the **Tool Settings** tab, select **MCU Post build outputs** and then choose **Convert to binary file (-O binary)**. Then, click on the **Apply and Close** button.
+
+{{< figure src="stcubeide-build-properties.png" alt="" >}}
+
+Now, you can build the project by right-clicking on it and selecting **Build Project** from the shortcut menu. Once the build is complete, the `.bin` file can be found in the `Debug` folder.
+
+Short the **BOOT0** pins on the GNSE board using a **shunt/jumper**. This allows programming GNSE through UART1 with the internal system bootloader of the STM32 MCU.
+
+{{< figure src="boot0.png" alt="" >}}
+
+Press and release the **RESET** button while shorting the **BOOT0**.
+
+GNSE will switch to the bootloader mode. Now unshort **BOOT0** by removing the **shunt/jumper** since it’s only being read at the startup.
+
+Start **STM32CubeProgrammar**.
+
+Select **UART** from the dropdown menu, and then choose the **COM port** associated with your GNSE.
+
+Click on the **Connect** button. 
+
+{{< figure src="uart-config.png" alt="" >}}
+
+After connecting, the button text will change to **Disconnect**. Also, the data in the device memory will display in the **Device memory** tab.
+
+{{< figure src="stcubeprog-connect.png" alt="" >}}
+
+Click on the **+** tab and select **Open file** from the menu.
+
+{{< figure src="stcubeprog-open-file.png" alt="" >}}
+
+Browse and select the `.bin` file, `basic.bin` for example.
+
+{{< figure src="browse-bin-file.png" alt="" >}}
+
+Click on the **Download** button.
+
+{{< figure src="stcubeprog-download.png" alt="" >}}
+
+It will take some time to download/flash the file onto the GNSE.
+
+{{< figure src="stcubeprog-download-progress.png" alt="" >}}
+
+Once completed click on the **OK** button.
+
+{{< figure src="stcubeprog-ok.png" alt="" >}}
+
+Click on the **Disconnect** button.
+
+Now you can remove the USB-to-UART converter from your GNSE.