small readme update

Author: kiryldz

README.md

@@ -47,14 +47,24 @@ Given an exisiting data class:
 For example:
 
 ```kotlin
+interface SampleInterface
+annotation class SampleAnnotation
+
 /**
  * Represents a person.
  * @property name The full name.
  * @property nickname The nickname.
  * @property age The age.
  */
 @DataCompat
-private data class PersonData(val name: String, val nickname: String? = null, val age: Int)
+@SampleAnnotation
+private data class PersonData(
+    @Default("\"John\"")
+    val name: String,
+    val nickname: String?,
+    @Default("42")
+    val age: Int
+) : SampleInterface
 ```
 
 After compilation, the following class will be generated: