Fix tutorial series link in package structure intro

[wenxiaojie1]

Summary

• Fix the "Start the tutorial series" button on the package structure intro page so it points from package-structure-code/intro.html to the tutorial intro page.
• The previous relative link resolved under the current section and caused the broken link reported in BUG: broken link pyopensci.github.io#899.

Validation

• Confirmed the updated relative link resolves to https://www.pyopensci.org/python-package-guide/tutorials/intro from https://www.pyopensci.org/python-package-guide/package-structure-code/intro.html.
• git diff --check

Closes pyOpenSci/pyopensci.github.io#899.

[agriyakhetarpal]

Hi @wenxiaojie1! I checked the CircleCI build output here, and the link now points to:

https://output.circle-artifacts.com/output/job/727caa47-3657-480e-ac48-8aa83d83f6c8/artifacts/0/html/tutorials/intro

Unfortunately, that is also broken. The correct link on CircleCI points to:

https://output.circle-artifacts.com/output/job/727caa47-3657-480e-ac48-8aa83d83f6c8/artifacts/0/html/tutorials/intro.html

This is not a CircleCI issue but rather that of a server behaviour difference with clean URLs that work on GitHub Pages, so let's add the file extension just to be safe, like how it is on other {button-link}s everywhere else. Thank you!

[wenxiaojie1]

Thanks for checking the rendered artifact. Updated the button link to use ../tutorials/intro.html explicitly.

[agriyakhetarpal]

Thanks for fixing this, @wenxiaojie1, this works now!