Update contributing, video section, add note on master to main

Describe the issue linked to the documentation

Videos on contributing to scikit-learn reference were created prior to renaming the branch name, and so refer to master, not main

Suggest a potential alternative/fix

In this file, under “Video Resources” section: https://github.com/scikit-learn/scikit-learn/blob/d01014c3198aafa336d9f8ed306f292d68c4a886/doc/developers/contributing.rst

add a note: Note: In January 2021, the default branch name for changed from master to main for scikit-learn to remove any unnecessary references to slavery and replace them with more inclusive terms. These videos were created prior to the renaming of the branch. For contributors who are viewing these videos to set up their working environment and submitting a PR, master should be replaced to main.

[reshamas]

@cesar-ca You are right about the link (not sure where I got that link from?).

The fix here would be to update the file contributing.rst under “Video Resources” section, adding this note:

Note: In January 2021, the default branch name for changed from master to main for scikit-learn to remove any unnecessary references to slavery and replace them with more inclusive terms. These videos were created prior to the renaming of the branch. For contributors who are viewing these videos to set up their working environment and submitting a PR, master should be replaced to main.

The goal here is that when contributors are setting up their environment, they should replace master to main.

It will be a while before @amueller and I record new videos.

[PSSF23]

Sorry for the people who came before me, but a doc change doesn’t need that long to implement~