Updating README to clarify that keys use attribute by default (#145)

README.md

@@ -104,7 +104,7 @@ vault_attribute :credit_card,
 - **Note** This value **cannot** be the same name as the vault attribute!
 
 #### Specifying a custom key
-By default, the name of the key in Vault is `#{app}_#{table}_#{column}`. This is customizable by setting the `:key` option when declaring the attribute:
+By default, the name of the key in Vault is `#{app}_#{table}_#{attribute}`. This is customizable by setting the `:key` option when declaring the attribute:
 
 ```ruby
 vault_attribute :credit_card,