docs(CHANGELOG.md): add breaking change for a9fcb0d (v1.2.13)

Closes #8909

Author: caitp

CHANGELOG.md

@@ -1989,6 +1989,13 @@ jQuery. We don't expect that app code actually depends on this accidental featur
     application if 100s of elements are being inserted into the page. Therefore after this
     change callbacks are only fired if registered on the element being animated.
 
+- **input:**
+  - due to [a9fcb0d0](https://github.com/angular/angular.js/commit/a9fcb0d0fc6456f80501b8820d02b04d7c15b6d6),
+    input[type=file] will no longer support ngModel. Due to browser support being spotty among target browsers,
+    file inputs cannot be cleanly supported, and even features which technically do work (such as ng-change)
+    work in an inconsistent way depending on the attributes of the form control.
+
+    As a workaround, one can manually listen for change events on file inputs and handle them manually.
 
 <a name="1.2.12"></a>
 # 1.2.12 cauliflower-eradication (2014-02-07)