doc: Add quickstart tutorial to bidsschematools site

[effigies]

This adds a jupytext notebook that can be also used as a RISE slideshow to introduce the basic interface of the bidsschematools package. Its target is downstream schema users.

Rendered: https://bidsschematools--2147.org.readthedocs.build/en/2147/quickstart.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.94%. Comparing base (460ad10) to head (97b126c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2147   +/-   ##
=======================================
  Coverage   81.94%   81.94%           
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  Files          17       17           
  Lines        1529     1529           
=======================================
  Hits         1253     1253           
  Misses        276      276           

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[bendhouseart]

My hero!

[yarikoptic]

@effigies do you recall why we need fsspec here? I do not see it used anywhere directly

[effigies]

For upath.