Add FiNER dataset
Hi,

this PR adds "A Finnish News Corpus for Named Entity Recognition" as new `finer` dataset.

The dataset is described in [this paper](https://arxiv.org/abs/1908.04212). The data is publicly available in [this GitHub](https://github.com/mpsilfve/finer-data).

Notice: they provide two testsets. The additional test dataset taken from Wikipedia is named as "test_wikipedia" split.
> That's really cool thank you !
> 
> Could you also add a dataset card ?
> You can find a template here : https://github.com/huggingface/datasets/blob/master/templates/README.md

The full information for adding a dataset card can be found here :) 
https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md#manually-tag-the-dataset-and-write-the-dataset-card
 Thanks your suggestions! I've fixed them, and currently working on the dataset card! @yjernite and @lhoestq I will add the dataset card a bit later in a separate PR if that's ok for you! Yes I want to re-emphasize if it was not clear that dataset cards are optional for the sprint. 

Only the tags are required for merging a datasets.

Please try to enforce this rule as well @lhoestq and @yjernite  Yes @stefan-it if you could just add the tags (the yaml part at the top of the dataset card) that'd be perfect :)  Oh, sorry, will add them now!
 Initial README file is now added :)  the `RemoteDatasetTest ` errors in the CI are fixed on master so it's fine merging since the CI is fixed on master