Add eHealth Knowledge Discovery dataset
Thank you very much for your review @lewtun ! 

I've updated the script metadata, created the README and fixed the two details you commented.

Ready for another review! 🤗  I've updated the task tag as we discussed and also added a couple of lines of code to make sure I include all the available examples.

Thank you again!
This Spanish dataset can be used to mine knowledge from unstructured health texts. 

In particular, for:
- Entity recognition
- Relation extraction
