Fix docker compose

[matthieubosquet]

The structure of the docker-compose is invalid.

This fixes it and allows easily running the website in a Docker container.

Dev workflow:

~/GitHub/solid ❯ git clone git@github.com:solid/solidproject.org.git
~/GitHub/solid ❯ cd solidproject.org/
~/GitHub/solid/solidproject.org ❯ docker compose up

The website gets built in _site/ and is visible at localhost:4000; jekyll running in the container watches the directory and rebuilds on changes.

[netlify]

✅ Deploy Preview for musical-sawine-26ffa9 ready!

Name	Link
🔨 Latest commit	6d089ea
🔍 Latest deploy log	https://app.netlify.com/projects/musical-sawine-26ffa9/deploys/68b0755c1842300008a3d144
😎 Deploy Preview	https://deploy-preview-926--musical-sawine-26ffa9.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[jeswr]

LGTM - thanks for assinging @Vinnl

I've just created an @solid/odi-team team so we can assign anyone on the ODI team for review going forward!