update change log with recent changes

Author: aaustin

ChangeLog.md

@@ -1,5 +1,13 @@
 Branch iOS SDK change log
 
+- v0.12.4 (WIP)
+  * setDebug must be called on getInstance. It's no longer a static method.
+  * referral code and promo code methods are no longer available
+  * action count methods are no longer available
+  * getReferralUrl removed - please migrate to BUO
+  * getContentUrl removed - please migrate to BUO
+  * BUO showShareSheet andCallback method deprecated - migrate to showShareSheet callback.
+
 - v0.12.3
   * Fabric Answers integration
   * Swift Testbed