Merge pull request #589 from landovsky/patch-1

Clarify effects of adding errors during execution

Author: AaronLasseigne

README.md

@@ -1221,6 +1221,8 @@ outcome.errors.details
 Detailed errors can also be manually added during the execute call by passing a
 symbol to `#add` instead of a string.
 
+Adding an error at any point during #execute will flag the interaction as invalid. The `#execute` method will, however, run to completion. Interaction started with `.run!` will raise `ActiveInteraction::InvalidInteractionError`.
+
 ``` rb
 def execute
   errors.add(:monster, :no_passage)