Branch point for 2020 Aug 29 Breaking Change

Update readme.md

Author: noroadsleft

readme.md

@@ -7,6 +7,12 @@
 [![GitHub contributors](https://img.shields.io/github/contributors/qmk/qmk_firmware.svg)](https://github.com/qmk/qmk_firmware/pulse/monthly)
 [![GitHub forks](https://img.shields.io/github/forks/qmk/qmk_firmware.svg?style=social&label=Fork)](https://github.com/qmk/qmk_firmware/)
 
+# THIS IS THE DEVELOP BRANCH
+
+Warning- This is the `develop` branch of QMK Firmware. You may encounter broken code here. Please see [Breaking Changes](https://docs.qmk.fm/#/breaking_changes) for more information.
+
+# Original readme continues
+
 This is a keyboard firmware based on the [tmk\_keyboard firmware](https://github.com/tmk/tmk_keyboard) with some useful features for Atmel AVR and ARM controllers, and more specifically, the [OLKB product line](https://olkb.com), the [ErgoDox EZ](https://ergodox-ez.com) keyboard, and the [Clueboard product line](https://clueboard.co).
 
 ## Documentation