Update CHANGELOG.md with GitHub PR #
IMPROVEMENTS:
-* Make `xray_index` attribute for local/remote/federated repository resources settable by users [GH-]
-* Add documentation for `xray_index` [GH-]
+* Make `xray_index` attribute for local/remote/federated repository resources settable by users [GH-330]
+* Add documentation for `xray_index` [GH-330]
## 2.20.0 (Feb 20, 2022)
