The latest contributing guide is available in the repository at
doc/developers/contributing.rst, or online at:
https://scikit-learn.org/dev/developers/contributing.html
There are many ways to contribute to scikit-learn. Improving the documentation is no less important than improving the code of the library itself. If you find a typo in the documentation, or have made improvements, do not hesitate to create a GitHub issue or preferably submit a GitHub pull request.
There are many other ways to help. In particular improving, triaging, and investigating issues, and reviewing other developers' pull requests are very valuable contributions that decrease the burden on the project maintainers.
Another way to contribute is to report issues you're facing, and give a "thumbs up" on issues that others reported and that are relevant to you. It also helps us if you spread the word: reference the project from your blog and articles, link to it from your website, or simply star it in GitHub to say "I use it".
Note that communications on all channels should respect our Code of Conduct.