use the theme options for pydata_sphinx_theme

[keewis]

• Closes No link to github from the docs #220

This is option 1 from #220 (comment): keep using pydata_sphinx_theme, but use the proper html theme options.

Edit: looks like the html_context options (github_user, github_repo, github_version, docs) are there to add a source edit link, which has to be enabled with use_edit_page_button.

For the link to github, we needed to add an icon link.

[TomNicholas]

Thanks @keewis ! This looks like it's working to me - ready to merge?

[keewis]

yep, go ahead