Add Big Patent dataset
@lhoestq reduced the dummy data size to around 19MB in total and added the dataset card. @lhoestq so I ended up removing all the nested JSON objects in the gz datafile and keep only one object with minimal content: `{"publication_number": "US-8230922-B2", "abstract": "dummy abstract", "application_number": "US-201113163519-A", "description": "dummy description"}`. 

They're reduced to 35KB in total (2.5KB per domain and 17.5KB for all domains), hopefully, they're small enough.
* More info on the dataset: https://evasharma.github.io/bigpatent/
* There's another raw version of the dataset available from tfds. However, they're quite large so I don't have the resources to fully test all the configs for that version yet. We'll try to add it later.