README.md in unidom-accession-1.0 vs README.md in unidom-accession-1.1

@@ -22,7 +22,10 @@
 The migration versions start with 200405.
 
 ## Call the Model
 ```ruby
 post_fulfillment = Unidom::Accession::PostFulfillment.valid_at.alive.first
-Unidom::Accession::PostFulfillment.fulfill! fulfiller: fulfiller, fulfilled: post, opened_at: Time.now
+
+post_fulfillment = Unidom::Accession::PostFulfillment.fulfill! fulfiller: fulfiller, fulfilled: post, opened_at: Time.now
+# or like the following source codes, which opened_at is optional
+post_fulfillment = Unidom::Accession::PostFulfillment.fulfill! fulfiller: fulfiller, fulfilled: post
 ```