Add a release note

Author: hichamboushaba

RELEASE-NOTES.txt

@@ -1,6 +1,10 @@
 *** PLEASE FOLLOW THIS FORMAT: [<priority indicator, more stars = higher priority>] <description> [<PR URL>]
 *** Use [*****] to indicate smoke tests of all critical flows should be run on the final APK before release (e.g. major library or targetSdk updates).
 *** For entries which are touching the Android Wear app's, start entry with `[WEAR]` too.
+21.3
+-----
+- [*] Switched to use `/wp/v2` for media uploads on Jetpack sites, this fixes media upload issues caused by XMLRPC problems [https://github.com/woocommerce/woocommerce-android/pull/12938]
+
 21.2
 -----
 - [**][Payments] Fixed a bug when IPP onboarding was not possible to finish from the app [https://github.com/woocommerce/woocommerce-android/pull/12917]