README.md in datacite-0.3.0 vs README.md in datacite-0.4.0

@@ -71,16 +71,28 @@
   -> response { response.doi },
   -> response { raise("Something went wrong", response.status) }
 )
 ```
 
+### Determine if a DOI exists
+
+```ruby
+result = client.exists?(id: '10.0001/bc123df4567')
+
+result.either(
+  -> response { response },
+  -> response { raise("Something went wrong", response.status) }
+)
+
+
 ### Validation
 This gem validates using a json schema from https://github.com/datacite/schema/blob/master/source/json/kernel-4.3/datacite_4.3_schema.json
 
 We've made the following changes:
   * relax the required fields (https://github.com/datacite/schema/issues/97)
   * add event property (https://github.com/datacite/schema/issues/100)
   * add url property (https://github.com/datacite/schema/issues/101)
+  * add xml property to support Datacite 4.4 xml schema via the api (https://github.com/datacite/schema/issues/99)
 
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.