[ENH,DOC] sphinx gallery binder

[jdkent]

• https://stanczakdominik.github.io/posts/simple-binder-usage-with-sphinx-gallery-through-jupytext/

Summary

Fixes #209.

List of changes proposed in this PR (pull-request)

• check here for build

[codecov[bot]]

Codecov Report

Merging #217 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #217   +/-   ##
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  Coverage   85.88%   85.88%           
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  Files          10       10           
  Lines         425      425           
  Branches       47       47           
=======================================
  Hits          365      365           
  Misses         50       50           
  Partials       10       10

[jdkent]

binder link appears at the bottom of example