Add #41 to changelog

Author: glennmatthews

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - #34 - in diff dicts, change keys `src`/`dst`/`_src`/`_dst` to `-` and `+`
 - #37 - add `sync_complete` callback, triggered on `sync_from` completion with changes.
+- #41 - add `summary` API for Diff and DiffElement objects.
 
 ## v1.0.0 - 2020-10-23