Add _id to model example

Author: sis0k0

models.py

@@ -12,6 +12,7 @@ class Config:
         allow_population_by_field_name = True
         schema_extra = {
             "example": {
+                "_id": "066de609-b04a-4b30-b46c-32537c7f1f6e",
                 "title": "Don Quixote",
                 "author": "Miguel de Cervantes",
                 "synopsis": "..."