Update CHANGELOG.md

CHANGELOG.md

 ### 1.0.12
-- get initial intent inside module, support rn 0.29.0 
+- get initial intent inside module, support rn 0.29.0 (for people upgrading from older version, change `new FIRMessagingPackage(getIntent())` back to `new FIRMessagingPackage()`)
 
 ### 1.0.11
 - change android library version to use 9.+ instead of 9.0.1 so it lives well with other libraries