Fix broken links to distillation on index page of documentation
# What does this PR do?

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Fixes broken links to DistilGPT2, DistilRoberta, and DistilmBERT on the homepage of documentation.

![image](https://user-images.githubusercontent.com/8587189/145648331-74d88898-137e-4f79-9b19-7b61de0e7eff.png)


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      Pull Request section?

## Who can review?
@sgugger

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@sgugger Running that command modifies `index.mdx` and resets the links back to the broken link. I'm not sure why that's the case.

![image](https://user-images.githubusercontent.com/8587189/145652891-5b315b7b-cad8-4581-b5fc-06fc937b3ae8.png)
<|||||>Ah you need to fix them in the main README, the rest is updated from it.<|||||>@sgugger Thank you, that makes sense. Do I need to apply these also to the language-specific READMEs or are those auto-generated?
![image](https://user-images.githubusercontent.com/8587189/145653451-040acf9b-6d52-4357-928a-c600d1cf5a73.png)
<|||||>If you run `make fix-copies`, all your changes should be propagated.<|||||>Hello @amitness, let us know if you'd like for us to run `make fix-copies` on your fork (and if so, please invite us as contributors so that we may push to it!)

Thanks!<|||||>@LysandreJik I have already run `make fix-copies` and there are no changes to any file after running it. The CI is still failing due to some other reason.

![image](https://user-images.githubusercontent.com/8587189/145996416-888fabc9-a865-4604-b18d-d07e4be15f22.png)

This [CI task](https://app.circleci.com/pipelines/github/huggingface/transformers/31179/workflows/4b5e0854-ff3f-4ccc-8669-1cf826a02e3d/jobs/321016) says the failure is due to code quality checks in docs, but my change is only switching the links in a README. Thoughts?<|||||>Ah, indeed the error says  the following:
```
Traceback (most recent call last):
  File "utils/style_doc.py", line 550, in <module>
    main(*args.files, max_len=args.max_len, check_only=args.check_only)
  File "utils/style_doc.py", line 538, in main
    raise ValueError(f"{len(changed)} files should be restyled!")
ValueError: 1 files should be restyled!

Exited with code exit status 1

```

Can you run `make fixup`, which should take care of everything style-related?<|||||>@LysandreJik Thank you. That worked and I have pushed all changes.<|||||>Thanks again for fixing!