Update README.md

Merge branch 'main' of https://huggingface.co/datasets/joelito/lextreme into main

added information about how to contribute

Update README.md (#4)

added lextreme citation

improved dataset card

Fix task tags (#2)

Fix task_ids (#1)

adapted dataset card

updated NER labelsets

added task overview

updated dataset card to conform with yaml

added first version of lextreme benchmark