Update website-navigation.qmd to use `_index.qmd`

[jameslairdsmith]

Two tweaks here would have helped me understand the "auto" option for creating navigation in websites a little bit better.

• Using _index.qmd instead of index.qmd because the latter creates its own page, which is often not what you want.
• Telling the user they can also control the order of a sub-directory using _index.qmd.

[cwickham]

/deploy-preview

[github-actions[bot]]

🚀 Deployed on https://deploy-preview-1181.quarto.org

[cderv]

Thanks. I am suprised by this _index.qmd usage. It is not something I was aware of it explicitly working. I would like to check this usage, because as soon as we document it it will be hard to change, and for now I wonder if this is something link to other thing.

Using a _ prefix in name like _index.qmd should mean that this document is excluded from render list for the project, so I am surprised setting metadata in it will be catched.