Update build docs from local copy

[sapols]

Our CircleCI deployment mechanism isn't production-ready anymore, but I found a manual workaround:

• Generate the build docs on my local machine by running tox -e build_gallery
• Copy the contents of the generated _build/html folder
  • After cleaning up any HTML output I don't like (e.g. deprecation warnings that reveal paths on my machine)
• Checkout the gh-pages branch
• Paste the contents of _build/html into the root project dir, replacing all conflicting files
  • This updates all the gallery website files

It's not a great workflow compared to an automated CI deploy, but this has the bonus benefit of my machine can run an X server so PyTplot's QT dependencies don't trip anything up.

[jibarnum]

This seems fine to me! 👍

[sapols]

@jibarnum just wanted to keep you in the loop.

[sapols]

Note to self: last time I updated gh-pages, to avoid overwriting the pytplot and pyspedas examples that are in a good state online but not locally, I cherry-picked/manually copied over the new files generated from the new example. See this PR.