switch Hindi-BERT to S3 README
The Markdown parser currently cuts off the CoLab URL (the last char is an underscore) on https://huggingface.co/monsoon-nlp/hindi-bert

There are some other necessary updates, and I'd rather update this model card by pushing to S3 in the future
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=h1) Report
> Merging [#6396](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/3e0fe3cf5c1059c04535de8f04f4efed7251adbe&el=desc) will **increase** coverage by `0.11%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/6396/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #6396      +/-   ##
==========================================
+ Coverage   79.40%   79.51%   +0.11%     
==========================================
  Files         148      148              
  Lines       27200    27200              
==========================================
+ Hits        21598    21628      +30     
+ Misses       5602     5572      -30     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/generation\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/6396/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3RmX3V0aWxzLnB5) | `86.71% <0.00%> (+7.51%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=footer). Last update [06bc347...106d0f3](https://codecov.io/gh/huggingface/transformers/pull/6396?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>@mapmeld we have a better version control/preview system coming in the future. In the meantime, merging this