Adding info that field.eval does not throw an error message to migration guide

Author: erikvansebille

docs/community/v4-migration.md

@@ -38,6 +38,7 @@ Version 4 of Parcels is unreleased at the moment. The information in this migrat
 ## Field
 
 - `Field.eval()` returns an array of floats instead of a single float (related to the vectorization)
+- `Field.eval()` does not throw OutOfBounds or other errors
 
 ## GridSet