renaming docs examples (#972)

* renaming docs examples

* tweaks

docs/examples/models_errors3.py

@@ -0,0 +1,19 @@
+from pydantic import BaseModel, PydanticValueError, ValidationError, validator
+
+class NotABarError(PydanticValueError):
+    code = 'not_a_bar'
+    msg_template = 'value is not "bar", got "{wrong_value}"'
+
+class Model(BaseModel):
+    foo: str
+
+    @validator('foo')
+    def name_must_contain_space(cls, v):
+        if v != 'bar':
+            raise NotABarError(wrong_value=v)
+        return v
+
+try:
+    Model(foo='ber')
+except ValidationError as e:
+    print(e.json())