README.md in czech_names_vocative-0.1.1 vs README.md in czech_names_vocative-0.2.0

@@ -21,9 +21,14 @@
 ## Usage
 
 ```ruby
 "Josef".vocative #=> "Josefe"
 "Petr".vocative #=> "Petře"
+"NonExistingName".vocativ! #=> nil
+
+"Josef".vocative! #=> "Josefe"
+"Petr".vocative! #=> "Petře"
+"NonExistingName".vocative! #=> "NonExistingName"
 ```
 
 ## Database
 
 Thanks for database to validace.cz