document ability to use Field() in create_model() (#1492)

pydantic/main.py

@@ -796,8 +796,10 @@ def create_model(
     :param __config__: config class to use for the new model
     :param __base__: base class for the new model to inherit from
     :param __validators__: a dict of method names and @validator class methods
-    :param **field_definitions: fields of the model (or extra fields if a base is supplied) in the format
-        `<name>=(<type>, <default default>)` or `<name>=<default value> eg. `foobar=(str, ...)` or `foobar=123`
+    :param **field_definitions: fields of the model (or extra fields if a base is supplied)
+        in the format `<name>=(<type>, <default default>)` or `<name>=<default value>, e.g.
+        `foobar=(str, ...)` or `foobar=123`, or, for complex use-cases, in the format
+        `<name>=<FieldInfo>`, e.g. `foo=Field(default_factory=datetime.utcnow, alias='bar')`
     """
     if __base__:
         if __config__ is not None: