NotFound [Error]: Not found: /

Hi doc-builder team!
Thanks for your great library!

I am trying to use your library to build docs for my own project, but I am facing some difficulties.
I have created a file structure for docs similar to what HuggingFace libraries have (`_toctree.yml`, etc.).

However, when I run `doc-builder preview LIBRARY_NAME PATH_TO_DOCS` and open web browser, I get a "NotFound [Error]: Not found: /" and web browser shows left side panel with the content from `_toctree.yml`, but in the center there is a page with 404 error.

At first, I thought that it might be related to some files missing (misconfiguration from my side), so I decided to try and preview docs from [peft library](https://github.com/huggingface/peft) and I get the same error when I run `doc-builder preview peft /workspaces/peft/docs/source`

Then I found issue #456 where they suggested using an older version of doc-builder, so I tried using 0.4.0 and the commits mentioned in that issue and nothing works for me. Do you have any idea how to fix this?

I used the [Dockerfile](https://github.com/huggingface/peft/blob/main/docker/peft-gpu/Dockerfile) from the `peft` project and installed nodejs like this:

```bash
curl -sL https://deb.nodesource.com/setup_16.x -o /tmp/nodesource_setup.sh
bash /tmp/nodesource_setup.sh
apt install nodejs -y

```