Adding changelog template

CHANGELOG.md

@@ -1,3 +1,23 @@
+x.x.x Release notes (yyyy-MM-dd)
+=============================================================
+### Enhancements
+* None.
+
+### Fixed
+* <How to hit and notice issue? what was the impact?> ([#????](https://github.com/realm/realm-js/issues/????), since v?.?.?)
+* None.
+
+### Compatibility
+* MongoDB Realm Cloud.
+* Realm Studio v11.0.0.
+* APIs are backwards compatible with all previous releases of Realm JavaScript in the 10.5.x series.
+* File format: generates Realms with format v22 (reads and upgrades file format v5 or later for non-synced Realm, upgrades file format v10 or later for synced Realms).
+
+### Internal
+* <Either mention core version or upgrade>
+* <Using Realm Core vX.Y.Z>
+* <Upgraded Realm Core from vX.Y.Z to vA.B.C>
+
 10.20.0-alpha.2 Release notes (2021-11-25)
 =============================================================
 NOTE: DO NOT USE THIS RELEASE IN PRODUCTION!