Ignore simlink
Author: sgugger
Pull request: yes

Didn't get an answer to my question on #4774 so asking again in the form of a PR ;-)

Currently, building the docs require making a simlink to the examples README (as per the [instructions](https://github.com/huggingface/transformers/tree/master/docs#building-the-documentation)) and that file then becomes untracked bit git. We should either ignore it (as proposed in this PR) or add it once for all (might be OS-dependent though). 

Happy to amend this PR to the second solution, I just don't like untracked files. :-)

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4796?src=pr&el=h1) Report
> Merging [#4796](https://codecov.io/gh/huggingface/transformers/pull/4796?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/acaa2e6267ebfda9814795fa00b6ad86c35ea5d6&el=desc) will **increase** coverage by `1.47%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4796/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4796?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4796      +/-   ##
==========================================
+ Coverage   74.59%   76.06%   +1.47%     
==========================================
  Files         128      128              
  Lines       21500    21500              
==========================================
+ Hits        16037    16355     +318     
+ Misses       5463     5145     -318     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4796?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `73.85% <0.00%> (-0.42%)` | :arrow_down: |
| [src/transformers/benchmark/benchmark\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9iZW5jaG1hcmsvYmVuY2htYXJrX3V0aWxzLnB5) | `43.57% <0.00%> (+0.35%)` | :arrow_up: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `87.36% <0.00%> (+1.10%)` | :arrow_up: |
| [src/transformers/trainer.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90cmFpbmVyLnB5) | `39.62% <0.00%> (+1.17%)` | :arrow_up: |
| [src/transformers/modeling\_xlnet.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ194bG5ldC5weQ==) | `75.69% <0.00%> (+2.29%)` | :arrow_up: |
| [src/transformers/modeling\_ctrl.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19jdHJsLnB5) | `98.64% <0.00%> (+2.71%)` | :arrow_up: |
| [src/transformers/tokenization\_transfo\_xl.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fdHJhbnNmb194bC5weQ==) | `40.67% <0.00%> (+3.87%)` | :arrow_up: |
| [src/transformers/modeling\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19yb2JlcnRhLnB5) | `95.69% <0.00%> (+10.04%)` | :arrow_up: |
| [src/transformers/modeling\_gpt2.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ19ncHQyLnB5) | `71.83% <0.00%> (+40.50%)` | :arrow_up: |
| [src/transformers/modeling\_tf\_pytorch\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4796/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl9weXRvcmNoX3V0aWxzLnB5) | `89.93% <0.00%> (+81.20%)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4796?src=pr&el=footer). Last update [acaa2e6...9ce1f67](https://codecov.io/gh/huggingface/transformers/pull/4796?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).


I let @LysandreJik check here, he knows better how to deal with the docs :-) 

Yes this sounds like a Windows-specific issue :)

Well having the symlink in the repo would certainly cause issues on Windows (since of course Linux symlinks are incompatible with Linux ones), but it's not linked to Windows, just to the doc-building setup :-p . 

I think this symbolic link is redundant with the `docs/source/examples.md@`. Since we commited the symbolic link, it would probably just be better to remove the instruction from the doc installation?

Eh, since I don't know how to read, I did not run the command in the right folder, hence the untracked file.
So yes, since the symbolic link is in the repo, there is no need to do anything! Closing this.