[model_cards] 🇹🇷 Add new (cased) BERTurk model
Hi,

this PR adds the model card for the (cased) community-driven 🇹🇷 BERTurk model.

Uncased model is coming soon!
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2879?src=pr&el=h1) Report
> Merging [#2879](https://codecov.io/gh/huggingface/transformers/pull/2879?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/6083c1566e261668a5de73cfe484c171ce232812?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2879/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2879?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #2879   +/-   ##
=======================================
  Coverage   75.06%   75.06%           
=======================================
  Files          94       94           
  Lines       15288    15288           
=======================================
  Hits        11476    11476           
  Misses       3812     3812
```



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[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/2879?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2879?src=pr&el=footer). Last update [6083c15...d18f775](https://codecov.io/gh/huggingface/transformers/pull/2879?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Looks good: https://huggingface.co/dbmdz/bert-base-turkish-cased