Update validator function name in examples to show that value must b… (#3327)

* Update validator function name in  examples to show that value must be bar vs must contain a space

* Add md file in

docs/examples/models_errors3.py

@@ -10,7 +10,7 @@ class Model(BaseModel):
     foo: str
 
     @validator('foo')
-    def name_must_contain_space(cls, v):
+    def value_must_equal_bar(cls, v):
         if v != 'bar':
             raise NotABarError(wrong_value=v)
         return v