[canvaskit] Add known swiftshader bug to Changelog

b/188239650

Change-Id: I371b24bc7210decd3cba22e6adc2432a688f0059
Bug: skia:11965
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/419156
Reviewed-by: Chris Dalton <csmartdalton@google.com>
diff --git a/modules/canvaskit/CHANGELOG.md b/modules/canvaskit/CHANGELOG.md
index fe6f9e4..e4b291b 100644
--- a/modules/canvaskit/CHANGELOG.md
+++ b/modules/canvaskit/CHANGELOG.md
@@ -19,6 +19,10 @@
    but can be an array, a TypedArray, or a MallocObj.
  - `CanvasKit.*Builder` have all been removed. Clients should use Malloc instead.
 
+### Known Bugs
+ - On legacy (non-ANGLE) SwiftShader, certain paths that require tessellation may not be drawn
+   correctly when using a WebGL-backed surface. (skbug.com/11965)
+
 ## [0.27.0] - 2021-05-20
 
 ### Added