[examples/flax] use Repository API for push_to_hub (#13672)

* use Repository for push_to_hub

* update readme

* update other flax scripts

* update readme

* update qa example

* fix push_to_hub call

* fix typo

* fix more typos

* update readme

* use abosolute path to get repo name

* fix glue script

examples/flax/README.md

@@ -61,3 +61,14 @@ For a complete overview of models that are supported in JAX/Flax, please have a
 
 Over 3000 pretrained checkpoints are supported in JAX/Flax as of May 2021.
 Click [here](https://huggingface.co/models?filter=jax) to see the full list on the 🤗 hub.
+
+## Upload the trained/fine-tuned model to the Hub
+
+All the example scripts support automatic upload of your final model to the [Model Hub](https://huggingface.co/models) by adding a `--push_to_hub` argument. It will then create a repository with your username slash the name of the folder you are using as `output_dir`. For instance, `"sgugger/test-mrpc"` if your username is `sgugger` and you are working in the folder `~/tmp/test-mrpc`.
+
+To specify a given repository name, use the `--hub_model_id` argument. You will need to specify the whole repository name (including your username), for instance `--hub_model_id sgugger/finetuned-bert-mrpc`. To upload to an organization you are a member of, just use the name of that organization instead of your username: `--hub_model_id huggingface/finetuned-bert-mrpc`.
+
+A few notes on this integration:
+
+- you will need to be logged in to the Hugging Face website locally for it to work, the easiest way to achieve this is to run `huggingface-cli login` and then type your username and password when prompted. You can also pass along your authentication token with the `--hub_token` argument.
+- the `output_dir` you pick will either need to be a new folder or a local clone of the distant repository you are using.