dataset(dgs): initial dataset loading script
Hi @AmitMY, 

Were you able to figure this out? I did not.
With all the limitations this repo currently has, I had to create a repo of my own using tfds to mitigate them. 
https://github.com/sign-language-processing/datasets/tree/master/sign_language_datasets/datasets/dgs_corpus

Closing as I don't know how to support this PR further
When trying to create dummy data I get:

> Dataset datasets with config None seems to already open files in the method `_split_generators(...)`. You might consider to instead only open files in the method `_generate_examples(...)` instead. If this is not possible the dummy data has t o be created with less guidance. Make sure you create the file dummy_data.

I am not sure how to manually create the dummy_data (what exactly it should contain)

Also note, this library says:
> ImportError: To be able to use this dataset, you need to install the following dependencies['pympi'] using 'pip install pympi' for instance'

When you actually need to `pip install pympi-ling`
