docs: add section on supported boards

www/docs/getting-started.md

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 Rugpi consists of two components, _Rugpi Bakery_ for building customized images, and _Rugpi Ctrl_ for maintaining and managing a Rugpi system.
 This quick start guide takes you through the steps necessary to build a custom Rugpi image with Rugpi Bakery.
 
-⚠️ **Note that Rugpi currently only supports 64-bit Raspberry Pi 4 and Compute Module 4.**
+⚠️ **Note that Rugpi currently only supports 64-bit Raspberry Pi 4/5 and Compute Module 4.**
+The template assumes that you are building an image for Raspberry Pi 4.
+For further details, please read the [Supported Boards](./guide/supported-boards.md) section of the user guide.
 
 ## Building an Image
 

www/docs/guide/supported-boards.md

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+---
+sidebar_position: 0
+---
+
+# Supported Boards
+
+Currently, Rugpi supports the following boards with the **64-bit** variant of Raspberry Pi OS:
+
+| Pi 5 | Pi 4 | Pi 3 | Pi 2 | Pi Zero 2 | Pi Zero   | CM 4 | CM 3 |
+|------|------|------|------|-----------|-----------|------|------|
+| ✅   | ✅   | ❌   | ❌   | ❌        | ❌        | ✅   | ❌   |
+
+**⚠️ Please also read the remarks for the respective boards bellow.**
+
+Rugpi relies on the [`tryboot` feature of Raspberry Pi's bootloader](https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#fail-safe-os-updates-tryboot), which is only supported from Raspberry Pi 4 onwards.
+There are plans to also support older boards without this feature.
+For further details, see [issue #4](https://github.com/silitics/rugpi/issues/4).
+
+Raspberry Pi OS releases based on Debian Bullseye and Bookworm are supported.
+
+
+### Raspberry Pi 4 and Compute Module 4
+
+The bootloader version shipped with Raspberry Pi 4 and Compute Module 4 does not support the `tryboot` feature out-of-the-box.
+To use Rugpi with these boards, the bootloader stored in the EEPROM must be updated to at least version `2023-05-11`.
+For Compute Module 4, this requires `usbboot` (see [CM4's documentation for details](https://www.raspberrypi.com/documentation/computers/compute-module.html#flashing-the-bootloader-eeprom-compute-module-4) or check out [this blog post by Jeff Geerling](https://www.jeffgeerling.com/blog/2022/how-update-raspberry-pi-compute-module-4-bootloader-eeprom)).
+For Raspberry Pi 4, you can set the `include_firmware = "pi4"` option in `rugpi-bakery.toml` to include the bootloader update in the image.
+The bootloader will then be automatically updated when first booting the image.
+Note that after the first boot, the automatic update will be disabled,[^1] i.e., you cannot take the SD card to another Raspberry Pi which does not yet have the update installed.
+
+[^1]: To prevent the EEPROM from being updated on each boot.