ABI compatibility to CHANGELOG for prev releases.

Bug: webm:1757
Change-Id: I19576aa0bc065045dcb0eaf770ae5b0d9ac9d684
diff --git a/CHANGELOG b/CHANGELOG
index cd4e8ba..4f5dcbd 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -36,6 +36,7 @@
   levels, and includes several improvements to NEON and numerous bug fixes.
 
   - Upgrading:
+    This release is ABI incompatible with the previous release.
     New codec control is added to get quantization parameters and loop filter
     levels.
 
@@ -61,6 +62,7 @@
   well as numerous bug fixes.
 
   - Upgrading:
+    This release is ABI incompatible with the previous release.
     New codec control is added to disable loopfilter for VP9.
 
     New encoder control is added to disable feature to increase Q on overshoot
@@ -91,6 +93,7 @@
   well as incremental improvements.
 
   - Upgrading:
+    This release is ABI compatible with the previous release.
     NV12 support is added to this release.
     A new interface is added for VP9 rate control. The new library libvp9rc.a
     must be linked by applications.
@@ -114,12 +117,14 @@
   This release collects incremental improvements to many aspects of the library.
 
   - Upgrading:
+    This release is ABI compatible with the previous release.
     ARCH_* defines have been removed in favor of VPX_ARCH_*.
 
 2019-07-15 v1.8.1 "Orpington Duck"
   This release collects incremental improvements to many aspects of the library.
 
   - Upgrading:
+    This release is ABI incompatible with the previous release.
     VP8E_SET_CPUUSED now accepts values up to 9 for vp9.
     VPX_CTRL_VP9E_SET_MAX_INTER_BITRATE_PCT had a spelling fix (was VP8E).
     The --sdk-path option has been removed. If you were using it to build for
@@ -138,7 +143,8 @@
   This release focused on encoding performance for realtime and VOD use cases.
 
   - Upgrading:
-    This adds and improves several vp9 controls. Most are related to SVC:
+    This release is ABI incompatible with the previous release. This adds and
+    improves several vp9 controls. Most are related to SVC:
       VP9E_SET_SVC_FRAME_DROP_LAYER:
         - Frame dropping in SVC.
       VP9E_SET_SVC_INTER_LAYER_PRED: