GitHub button in page header links to production repo only

[sanchuanhehe]

Description

The GitHub logo/button in the top-right corner of the built documentation pages currently links to the production repository's issue tracker. This is misleading for users who want to file issues about the guidebook's editorial content.

Suggested Fix

The GitHub link area should point to both repositories so users can navigate to the appropriate one:

• theopensourceway/guidebook — for editorial content, translation, and documentation issues
• theopensourceway/production — for build toolchain, CI, and theme issues

This could be implemented by:

1. Changing the default GitHub link to point to the guidebook repo (since most user-facing issues will be editorial)
2. Adding a secondary link or dropdown that also references the production repo
3. Configuring html_theme_options in conf.py to set appropriate repository_url and potentially adding a custom link

In Sphinx Book Theme, the relevant config options are:

html_theme_options = {
    "repository_url": "https://github.com/theopensourceway/guidebook",
    "use_repository_button": True,
    # Consider also linking to production repo
}