DOC: update the CategoricalIndex docstring
Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

- [X] PR title is "DOC: update the <your-function-or-method> docstring"
- [X] The validation script passes: `scripts/validate_docstrings.py <your-function-or-method>`
- [X] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] The html version looks good: `python doc/make.py --single <your-function-or-method>`
- [X] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

```
################################################################################
################################## Validation ##################################
################################################################################

Errors found:
        No returns section found
        No examples section found
```

The documentation has been improved. The function actually refers to a function defined elsewhere. Therefore, we decided to include a "see also" section. 

Same message for CategoricalIndex.codes, CategoricalIndex.ordered and CategoricalIndex.categories.

Hello @Adrienlq! Thanks for updating the PR.

 - In the file [`pandas/core/indexes/category.py`](https://github.com/pandas-dev/pandas/blob/e38c4d4063cbece61fb8989515f9416240bb5778/pandas/core/indexes/category.py), following are the PEP8 issues :

> [Line 386:80](https://github.com/pandas-dev/pandas/blob/e38c4d4063cbece61fb8989515f9416240bb5778/pandas/core/indexes/category.py#L386): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (82 > 79 characters)



##### Comment last updated on March 12, 2018 at 09:05 Hours UTC @Adrienlq any reason you are closing this? Hello, sorry I have very few experience with github. I thought the PR was a failure so I closed it.
What is the status of the PR ? Should I do something now ?
Thank you @Adrienlq The PR is certainly not a failure! It's a good start, but with some to do's. I added comments about that, and if you would like to further work on it, you can make changes based on this feedback, add this as a commit in your branch, and push this to github, which will automatically update this PR. 

See https://python-sprints.github.io/pandas/guide/pandas_pr.html#updating-a-pull-request for some more detailed information closing as stale. if you'd like to continue pls ping.