Update RELEASE-NOTES.txt

Author: itsmeichigo

RELEASE-NOTES.txt

@@ -10,6 +10,7 @@
 - [*] Background image upload: Fix issue showing uploaded images while saving is in progress [https://github.com/woocommerce/woocommerce-ios/pull/15107]
 - [*] Background image upload: Fix missing error notice in iPhones [https://github.com/woocommerce/woocommerce-ios/pull/15117]
 - [*] Filters applied in product selector no longer affect the main product list screen. [https://github.com/woocommerce/woocommerce-ios/pull/14764]
+- [**] Product Images: Update error handling [https://github.com/woocommerce/woocommerce-ios/pull/15105]
 
 21.7
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