update docs

CHANGES.md

@@ -1,6 +1,21 @@
 # CHANGES
 
-## v4.2.21-RC
+## v4.3.0-RC
+
+### BREAKING CHANGES
+
+None.
+
+Upgrading Guide: <https://docs.growi.org/en/admin-guide/upgrading/43x.html>
+
+### Updates
+
+* Feature: New Slack Integration with Slack Bot
+    * Searching GROWI pages from Slack
+    * Creating GROWI pages from Slack
+        * Easy record conversations
+
+## v4.2.21
 
 * Improvement: Headers style on built-in editor
 * Improvement: Codemirror is now scrollable one editor height of empty space into view at the bottom of the editor