add link to zephyr device tree

Add a link to zephyr device trees that can be used to write firmware with zephyr[0] on the badge

[0]: https://zephyrproject.org/

Author: kloenk

README.md

@@ -19,6 +19,7 @@ In addition to the LoRa module, there are 5 RGB LEDs on the side, a qwiic/Stemma
 Feel free to submit a PR adding on to this list with your project that runs on the badge.
 
 - [Initial Meshtastic firmware](https://github.com/badgeteam/bornhack2025-meshtastic) ([Flasher tool](https://github.com/badgeteam/bornhack2025-flasher))
+- [Zephyr device tree](https://cyberchaos.dev/kloenk/bornhack-2025-badge) (no actually firmware, just support files)
 - _project name and link to more info_
 
 
@@ -34,4 +35,4 @@ The hardware design of the `main` branch of this repository is released under th
 * the "Creative Commons Attribution-ShareAlike 4.0 International License"
   (CC BY-SA 4.0) full text of this license is included in the LICENSE file
   and a copy can also be found at
-  [http://creativecommons.org/licenses/by-sa/4.0/](http://creativecommons.org/licenses/by-sa/4.0/)
+  [http://creativecommons.org/licenses/by-sa/4.0/](http://creativecommons.org/licenses/by-sa/4.0/)