Add a note about clang-format to the changelog

docs/ChangeLog/20190830.md

@@ -4,6 +4,12 @@ Four times a year QMK runs a process for merging Breaking Changes. A Breaking Ch
 
 This document marks the inaugural Breaking Change merge. A list of changes follows.
 
+## Core code formatting with clang-format
+
+* All core code (`drivers/`, `quantum/`, `tests/`, and `tmk_core`) has been formatted with clang-format
+* A travis process to reformat PR's on merge has been instituted
+* You can use the new CLI command `qmk cformat` to format before submitting your PR if you wish.
+
 ## LUFA USB descriptor cleanup
 
 * Some code cleanups related to the USB HID descriptors on AVR keyboards, to make them easier to read and understand