Provide documentation or an example on how to use subclassing to filter fields from being included in the Diff

### Environment
* DiffSync version:  1.6.0

### Proposed Functionality

Provide documentation or an example on how to use subclassing to filter fields from being included in the Diff.

### Use Case

Make it easier to provide a common set of models from which users of these models can subclass and change the models to address their specific usecase. 