Release Notes: add new section for next version (20.6)

Author: wpmobilebot

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 IPA before release (e.g. major library or OS update).
 
+20.6
+-----
+
+
 20.5
 -----
 - [*] Blaze: Schedule a reminder local notification asking to continue abandoned campaign creation flow. [https://github.com/woocommerce/woocommerce-ios/pull/13950]