DOC: Add fMRI tutorial

[scott-huberty]

Borrowed from NiLearn's CanICA tutorial

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.72%. Comparing base (d82ae7e) to head (749854f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #67      +/-   ##
==========================================
- Coverage   90.93%   90.72%   -0.21%     
==========================================
  Files          21       21              
  Lines        1467     1467              
  Branches      138      138              
==========================================
- Hits         1334     1331       -3     
- Misses         83       85       +2     
- Partials       50       51       +1     

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