add cleanlab to awesome-transformers tools list
This PR adds the cleanlab package to the awesome-transformers list.  

cleanlab uses **transformers** & Hugging Face in all sorts of ways. Here's a couple of them:
- [tutorial for text data with **transformers**](https://docs.cleanlab.ai/stable/tutorials/datalab/text.html)
- [active learning with **transformers**](https://github.com/cleanlab/examples/blob/master/active_learning_transformers/active_learning.ipynb)
- [auditing data in the  **datasets** format](https://github.com/cleanlab/examples/blob/master/datalab_image_classification/datalab.ipynb), which is now the [primary data format](https://docs.cleanlab.ai/stable/cleanlab/datalab/datalab.html) supported by cleanlab
- [how to wrap a **transformers** model to be sklearn compatible](https://github.com/cleanlab/examples/blob/master/transformer_sklearn/transformer_sklearn.ipynb)

I'm not sure which reviewer is most appropriate, but perhaps one of the listed documentation reviewers: 
@sgugger, @stevhliu or @MKhalusova


Also ccing @LysandreJik who compiled the list :)<|||||>_The documentation is not available anymore as the PR was closed or merged._