next part of the docs and api documentation in beta ver

docs/api/fields/decorators.md

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+<a name="decorators.property_field"></a>
+# decorators.property\_field
+
+<a name="decorators.property_field.property_field"></a>
+#### property\_field
+
+```python
+property_field(func: Callable) -> Union[property, Callable]
+```
+
+Decorator to set a property like function on Model to be exposed
+as field in dict() and fastapi response.
+Although you can decorate a @property field like this and this will work,
+mypy validation will complain about this.
+Note that "fields" exposed like this do not go through validation.
+
+**Raises**:
+
+- `ModelDefinitionError`: if method has any other argument than self.
+
+**Arguments**:
+
+- `func (Callable)`: decorated function to be exposed
+
+**Returns**:
+
+`(Union[property, Callable])`: decorated function passed in func param, with set __property_field__ = True
+