Updated README

README.md

@@ -236,13 +236,25 @@ The `create(...)` method accepts an `Into` clause which specifies the entity for
 
     let person = transaction.create(Into(MyPersonEntity))
 
-While the syntax is simple, CoreStore does not just naively insert a new object. This single line does the following:
+While the syntax is straightforward, CoreStore does not just naively insert a new object. This single line does the following:
 - Checks that the entity type exists in any of the transaction's parent persistent store
 - If the entity belongs to only one persistent store, a new object is inserted into that store and returned from `create(...)`
-- If the entity does not belong to any store, an assert will be triggered. This is a programmer error and should never occur in production code.
+- If the entity does not belong to any store, an assert will be triggered. **This is a programmer error and should never occur in production code.**
+- If the entity belongs to multiple stores, an assert will be triggered. **This is also a programmer error and should never occur in production code.** Normally, with Core Data you can insert an object in this state but saving the `NSManagedObjectContext` will always fail. CoreStore checks this for you at creation time where it makes sense (not during save).
+
+If the entity exists in multiple configurations, you need to provide the configuration name for the destination persistent store:
+
+    let person = transaction.create(Into<MyPersonEntity>("Config1"))
+
+or if the persistent store is the auto-generated "Default" configuration, specify `nil`:
+
+    let person = transaction.create(Into<MyPersonEntity>(nil))
+
+Note that if you do explicitly specify the configuration name, CoreStore will only try to insert the created object to that particular store and will fail if that store is not found; it will not fall back to any other store the entity belongs to. 
 
 ### Updating objects
 
+
 ### Deleting objects
 
 ## <a name="fetch_query"></a>Fetching and querying