Update CHANGELOG.md

Author: rekby

CHANGELOG.md

@@ -1,3 +1,12 @@
+COMPLETE CHANGELOG FROM v2:
+* Add api for topic service
+
+BROKEN CHANGES:
+* deny any action in transaction after commit/rollback (switch to old behaviour with ydb.global_allow_split_transactions(True))
+* raise exception for truncated response by default (switch to old behavior with ydb.global_allow_truncated_result(True))
+* drop support python 2
+* Use anonymous credentials for auth by default instead of iam metadata (use ydb.driver.credentials_from_env_variables for creds by env var)
+
 ## 3.0.1b13 ##
 * Fixed commit for sync reader
 * Group messages while send to server