Use a command class's `__doc__` if `overview` does not exist

### What needs to get done

The `overview` attribute is often duplicative of a command class's docstring. If the `overview` attribute doesn't exist, use the command's docstring instead.

### Why it needs to get done

Helps make automatic documentation better, since it'll display the command docs.

Locate the command overview handling and automatic documentation generation described in the issue. Verify how commands without an overview are currently documented; done means their __doc__ text is used and appears in the generated command documentation.

Written by the indexing model from the issue text.