[jacky_studio/piggy60] warn about incompatible PCB rev (#20232)

keyboards/jacky_studio/piggy60/readme.md

@@ -5,7 +5,8 @@
 A gasket-mounted 60% in the style of the S7 Elephant.
 
 * Keyboard Maintainer: [The QMK Community](https://github.com/qmk)
-* Hardware Supported: Piggy60
+* Hardware Supported: Piggy60 PCB "rev1" (atmega32u4)
+  * **Make sure your PCB uses an `atmega32u4` before flashing!** A PCB that uses an `APM32F103CBT6` with `uf2boot` has been shipped with some extras purchases and to replace some defective units. Flashing that PCB with "rev1" firmware may result in a non-functional PCB which can only be recovered using a hardware programmer (e.g. an ST-Link V2)
 * Hardware Availability: Group Buy took place between 2021-05-22 1600 UTC and 2021-05-25 1600 UTC on [https://jackylab.com/](https://jackylab.com/).
 
 Make example for this keyboard (after setting up your build environment):