Update modelcard of bert-base-german-cased
Add image
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2951?src=pr&el=h1) Report
> Merging [#2951](https://codecov.io/gh/huggingface/transformers/pull/2951?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/3e98f27e4a9bb0ac3d0fe24b94d30da42cdae8a7?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/2951/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2951?src=pr&el=tree)

```diff
@@          Coverage Diff           @@
##           master   #2951   +/-   ##
======================================
  Coverage    76.1%   76.1%           
======================================
  Files          98      98           
  Lines       15946   15946           
======================================
  Hits        12136   12136           
  Misses       3810    3810
```



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[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/2951?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/2951?src=pr&el=footer). Last update [3e98f27...d3f1583](https://codecov.io/gh/huggingface/transformers/pull/2951?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
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