Train T5 in Tensoflow 2 Community Notebook
# What does this PR do?
This adds a link to **Training T5 in Tensoflow 2 Community Notebook** under the notebooks/Readme.md community notebook section.  

This notebook demonstrates how to train T5 for any task using Tensorflow 2. Trains a Question & Answer task implemented in Tensorflow 2 using SQUAD


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dimiss the other checks if that's the case). **Yes**
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests), 
      Pull Request section? **Yes**
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to the it if that's the case. [Forum Link](https://discuss.huggingface.co/t/how-to-train-t5-with-tensorflow/641)
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation). **Not Applicable**
- [ ] Did you write any new necessary tests?  **Not Applicable**


## Who can review?
@patrickvonplaten @jplu

Hello!

Thanks a lot for your awesome notebook! Just two tiny updates, can you clean your list of imports and use `datasets` instead of `tfds`?<|||||>@jplu  much appreciated. i will clean up the imports. by datasets do you mean an alias for tensorflow datasets instead of tfds?<|||||>No, I mean using https://github.com/huggingface/datasets instead.<|||||>@jplu  i have done the necessary changes. I have also switched to  [datasets](https://github.com/huggingface/datasets) as requested. for this i have created a [new colab notebook](https://colab.research.google.com/github/snapthat/TF-T5-text-to-text/blob/master/snapthatT5/notebooks/TF-T5-Datasets%20Training.ipynb) which uses datasets as its primary source.<|||||># [Codecov](https://codecov.io/gh/huggingface/transformers/pull/7428?src=pr&el=h1) Report
> Merging [#7428](https://codecov.io/gh/huggingface/transformers/pull/7428?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/f62f2ffdcc2df75cf01438bebc7ae281d921d21d?el=desc) will **increase** coverage by `0.48%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/7428/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/7428?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #7428      +/-   ##
==========================================
+ Coverage   78.17%   78.66%   +0.48%     
==========================================
  Files         181      181              
  Lines       35800    35800              
==========================================
+ Hits        27986    28161     +175     
+ Misses       7814     7639     -175     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/7428?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/modeling\_tf\_electra.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9lbGVjdHJhLnB5) | `24.25% <0.00%> (-73.56%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_lxmert.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9seG1lcnQucHk=) | `22.14% <0.00%> (-72.41%)` | :arrow_down: |
| [src/transformers/modeling\_rag.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19yYWcucHk=) | `25.32% <0.00%> (-51.72%)` | :arrow_down: |
| [src/transformers/modeling\_tf\_xlm.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl94bG0ucHk=) | `58.52% <0.00%> (-34.74%)` | :arrow_down: |
| [src/transformers/modeling\_marian.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19tYXJpYW4ucHk=) | `60.00% <0.00%> (-30.00%)` | :arrow_down: |
| [src/transformers/modeling\_longformer.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19sb25nZm9ybWVyLnB5) | `74.14% <0.00%> (-18.70%)` | :arrow_down: |
| [src/transformers/tokenization\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fYXV0by5weQ==) | `83.58% <0.00%> (-8.96%)` | :arrow_down: |
| [src/transformers/activations.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9hY3RpdmF0aW9ucy5weQ==) | `79.16% <0.00%> (-4.17%)` | :arrow_down: |
| [src/transformers/configuration\_rag.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3JhZy5weQ==) | `97.77% <0.00%> (-2.23%)` | :arrow_down: |
| [src/transformers/modeling\_bart.py](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19iYXJ0LnB5) | `94.10% <0.00%> (-0.51%)` | :arrow_down: |
| ... and [19 more](https://codecov.io/gh/huggingface/transformers/pull/7428/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/7428?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/7428?src=pr&el=footer). Last update [f62f2ff...d9df829](https://codecov.io/gh/huggingface/transformers/pull/7428?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Awesome!! Thanks a lot for your notebook!!<|||||>Thanks a lot @HarrisDePerceptron the community has been asking about such a notebook for a long time :-) <|||||>Thanks @patrickvonplaten  !! it was long over due :)