Update CHANGELOG.md

Author: brizental

CHANGELOG.md

@@ -5,6 +5,9 @@
 * [#411](https://github.com/mozilla/glean.js/pull/411): Tag all messages logged by Glean with the component they are coming from.
 * [#399](https://github.com/mozilla/glean.js/pull/399): Check if there are ping data before attempting to delete it.
   * This change lowers the amount of log messages related to attempting to delete inexistent data.
+* [#415](https://github.com/mozilla/glean.js/pull/415): Gzip ping paylod before upload
+  * This changes the signature of `Uploader.post` to accept `string | Uint8Array` for the `body` parameter, instead of only `string`.
+  * The gizpping functionality is disabled in Qt/QML environments. Follow [Bug 1716322](https://bugzilla.mozilla.org/show_bug.cgi?id=1716322) for updates on the status of this feature on that platform.
 
 # v0.15.0 (2021-06-03)