README_V3.md in schemacop-3.0.23 vs README_V3.md in schemacop-3.0.24

@@ -107,9 +107,19 @@
 * `examples`: Here, you can provide examples which will be valid for the schema
 * `enum`: Here, you may enumerate values which will be valid, if the provided
   value is not in the array, the validation will fail
 * `default`: You may provide a default value for items that will be set if the
   value is not given
+* `require_key`: If set to true, validate that the key of this node is present, 
+  regardless of the value (including `nil`). This is only validated if the 
+  schema type is set to `:hash`.
+  Example:
+  ```ruby
+  Schemacop::Schema3.new(:hash) do
+    str? :foo, require_key: true
+    int? :bar, require_key: true
+  end
+  ```
 
 The three keywords `title`, `description` and `examples` aren't used for validation,
 but can be used to document the schema. They will be included in the JSON output
 when you use the `as_json` method: