Add add_schema example

Author: Adrian Dankiv

example1_simple.py

@@ -16,7 +16,7 @@ class Config:
     bulk_size: int = 20
 
 
-Config.Schema = class_schema(Config)
+Config.Schema = class_schema(Config)  # <--------------
 
 json_data = {
     'file_path': '/validators-example/file',

example1_simple_add_schema.py

@@ -0,0 +1,31 @@
+from dataclasses import dataclass, field
+from enum import Enum
+
+from marshmallow_dataclass import add_schema
+
+
+class Command(Enum):
+    CREATE = 'create'
+    DELETE = 'delete'
+
+
+@add_schema  # <--------------
+@dataclass
+class Config:
+    file_path: str
+    command: Command = field(metadata=dict(by_value=True))
+    bulk_size: int = 20
+
+
+json_data = {
+    'file_path': '/validators-example/file',
+    'command': 'create',
+}
+
+config = Config.Schema().load(json_data)
+print(config)
+print(Config.Schema().dump(config))
+
+assert config.file_path == '/validators-example/file'
+assert config.command is Command.CREATE
+assert config.bulk_size == 20