Tensorflow not found but i can import it
## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->

- `transformers` version: 4.4.0.dev0
- Platform: macOS-11.2.1-arm64-arm-64bit
- Python version: 3.8.6
- PyTorch version (GPU?): not installed (NA)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: <fill in>
- Using distributed or parallel set-up in script?: <fill in>


@jplu, @patrickvonplaten, @LysandreJik 

## Description
When i import transformers i get message bellow.

## To reproduce

Steps to reproduce the behavior:

1. install tf for mac m1(https://github.com/apple/tensorflow_macos)
2. install transformers
3. import transformers


Message when i import transformers:
```
None of PyTorch, TensorFlow >= 2.0, or Flax have been found. Models won't be available and only tokenizers, configuration and file/data utilities can be used.
```

## Expected behavior
I'd like to make transformers find tensorflow.

What is the output of:
```
import tensorflow
print(tensorflow.__version__)
```
?<|||||>> What is the output of:
> 
> ```
> import tensorflow
> print(tensorflow.__version__)
> ```
> 
> ?

'2.4.0-rc0'<|||||>Hello!

We currently don't support other implementations than the Google's pypi versions. The reason is because we don't tests on other versions and then we cannot guarantee it will works on those "extra" versions.

To make `transformers` works on Mac I suggest you to use the official version of TensorFlow as proposed in their documentation https://www.tensorflow.org/install/pip<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.