Add XDF to "Reading EEG data" tutorial

[cbrnr]

Closes #5180.

Besides tidying up and improving the docstring a bit, I have added a section on how to import XDF data.

[sappelhoff]

LGTM, three nitpicks

[cbrnr]

Any idea why CircleCI is not showing up?

[larsoner]

No idea, it doesn't show up in https://app.circleci.com/pipelines/github/mne-tools/mne-python and even when I try to force it using https://app.circleci.com/pipelines/github/mne-tools/mne-python?branch=pull%2F9289 it doesn't show up. Sometimes in the past CircleCI has had problems when people forked and then enabled builds on their fork, did you mess with any of your own GitHub user's CircleCI settings recently?

[cbrnr]

Hm, maybe I changed some CircleCI setting accidentally when I was cleaning out (supposedly) unused apps. Do you know where I need to look?

[larsoner]

I have CircleCI listed in "Authorized OAuth Apps" in https://github.com/settings/applications. Also you can try navigating to something like https://app.circleci.com/pipelines/github/mne-tools/mne-python/7809/workflows/d85b7b1f-5a4f-4193-bd35-68d6b582e243/jobs/27188/artifacts, I think CircleCI only lets you do it if you have given it some permissions.

[cbrnr]

I didn't have CircleCI in my list of authorized apps. Following the link did prompt me to log in, which in turn created the entry again. Thanks @larsoner! I'll create some dummy commit to trigger the build.

[cbrnr]

Rendered doc looks good: https://27223-1301584-gh.circle-artifacts.com/0/dev/auto_tutorials/io/plot_20_reading_eeg_data.html#sphx-glr-auto-tutorials-io-plot-20-reading-eeg-data-py

@larsoner @drammock ready for review.

[cbrnr]

@drammock not directly related to this PR, but the TOC link "Setting EEG references" never gets highlighted (not even if I click on it). Maybe it's because the corresponding text is too little, but I think it would be nice if it highlighted at least when clicking it.

Edit: clicking on the various entries in the TOC seems broken, not just the link I mentioned. Clicking some links takes me to a different section.

[larsoner]

I added this tiny proof-of-concept example:

• https://27538-1301584-gh.circle-artifacts.com/0/dev/auto_tutorials/io/plot_20_reading_eeg_data.html#xdf-data-xdf-xdfz
• https://27538-1301584-gh.circle-artifacts.com/0/dev/auto_examples/io/plot_read_xdf.html

+1 for merge from me

[larsoner]

@drammock can you see if you're happy with the structure now?

[drammock]

other than 2 small details LGTM

[larsoner]

Thanks @cbrnr !