Add language and license information to model cards
Should fix issues #3397 and #3357 
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/3864?src=pr&el=h1) Report
> Merging [#3864](https://codecov.io/gh/huggingface/transformers/pull/3864?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/a21d4fa410dc3b4c62f93aa0e6bbe4b75a101ee9&el=desc) will **increase** coverage by `0.00%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/3864/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/3864?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #3864   +/-   ##
=======================================
  Coverage   78.61%   78.62%           
=======================================
  Files         106      106           
  Lines       17953    17953           
=======================================
+ Hits        14114    14115    +1     
+ Misses       3839     3838    -1     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/3864?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/3864/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `92.76% <0.00%> (+0.16%)` | :arrow_up: |

------

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<|||||>Hi @julien-c !

I hope you are well. My pull request is ready for review.

I have tried my best to add license and language information to all model cards. I have added a few model cards as well.

Note that my changes may have some downstream consequences:
- the addition of a "license" key, the value being an atomic list)
- the normalization of the "languages" key (I added the "s"), the value being a list of [ISO 639-1 codes](https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes). For multilingual BERT, I had to simplify some rare languages by merging it with its ISO "macro code" (example: "South Azerbaijani" -> "az", "Bavarian" -> "de")
 
On the website, you may want to read those values and render them back in human-readable form.

Cheers,

Alex
<|||||>Hi Alex,

as mentioned in the previous issue, I'd rather use identifiers listed in https://help.github.com/en/github/creating-cloning-and-archiving-repositories/licensing-a-repository

I can probably search and replace though.

Also, you pushed whitespace changes which make reviewing the actual changes slightly tedious.<|||||>[EDIT] Sure, I have replaced licenses with these identifiers! 
For whitespaces, I have autoformatting activated on sublime, that's why. Sorry for the inconvenience. <|||||>Good morning @julien-c,

I hope all is well. What do you think of this PR?

Cheers,

Alex<|||||>I'm doing a partial merge (retaining your authorship information, @alexcombessie) of the licenses, as the languages will require some backend changes.

(I'll do a search and replace at a later point)

Thank you for your contribution