Add warning to Departure::Migration

Author: xjunior

lib/departure/migration.rb

@@ -63,6 +63,9 @@ def migrate(direction)
 
     # Includes the Foreigner's Mysql2Adapter implemention in
     # DepartureAdapter to support foreign keys
+    #
+    # Warning: Foreigner only works with MySQL2, and therefore
+    #          trilogy is not supported
     def include_foreigner
       Foreigner::Adapter.safe_include(
         :DepartureAdapter,