update tutorial with best practices and Black formatting

[bendichter]

Motivation

fix #1628

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

Merging #1656 (cc01d29) into dev (dd54e5a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1656   +/-   ##
=======================================
  Coverage   91.93%   91.93%           
=======================================
  Files          26       26           
  Lines        2592     2592           
  Branches      497      477   -20     
=======================================
  Hits         2383     2383           
  Misses        134      134           
  Partials       75       75           

Flag	Coverage Δ
integration	71.52% <ø> (ø)
unit	83.56% <ø> (ø)

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[rly]

I ran black and isort on the gallery files and updated requirements-dev.txt. This looks good to go. Thanks!