Python: Clarify if order of docstring sections is fixed

The python style guide mentions the docstring sections `Args`, `Returns/Yields` and `Raises` but does not clearly specify whether their order is enforced.

All examples show
```
Args: ...

Returns: ...

Raises: ...
```

Should this be taken as the only acceptable order? Or would e.g. `Raises:` before `Returns:` be allowed?

Question arose in https://github.com/danymat/neogen/pull/194