update docs

Author: justin-tay

doc/migration-2.0.0.md

@@ -9,8 +9,11 @@
 
 ### Major Changes
 
-- Removal of deprecated methods and functionality from 1.x
-- Major renaming of many of the public APIs and moving of classes into sub-packages
+- Removal of deprecated methods and functionality from 1.x.
+- Major renaming of many of the public APIs and moving of classes into sub-packages.
+- Errors are returned as a `List` instead of a `Set`.
+- External resources will not be automatically fetched by default. This now requires opt-in via configuration. 
+  - This is to conform to the specification that requires such functionality to be disabled by default to prefer offline operation. Note however that classpath resources will still be automatically loaded.
 
 #### Renaming and Refactoring