Change homepage / display sidebar on homepage

[dichotommy]

We have known for some time that requiring an additional click from users who land on docs.meilisearch.com to access any actual documentation content—or simply see what is available—is a bad practice. It introduces unnecessary friction for users who navigate to the homepage frequently. Sadly, Vuepress does not provide any convenient mechanism for using a custom homepage—it requires an index.md file to be present at root which is built into the homepage (at least, AFAIK).

Two potential solutions

The "easiest" solution would be redirecting docs.meilisearch.com to a specific page such as /learn/getting_started/quick_start.md. However using redirects to hide pages we don't like strikes me as incredibly sloppy and a bad idea, so let's not do this 😬

I think our best option is adding the /learn sidebar to index.md somehow. I am not sure if this is possible, but it's worth a try. Failing that, we will have to consider more radical options.

More radical options

We could redo our entire file hierarchy so all documentation pages are in the same folder and thus use the same sidebar. This is probably overkill to solve this problem, but on the other hand, may provide other benefits. Keeping all of our markdown content in the same folder would mean that we no longer have to move a file, update links, and add redirects every time we want to change our content organization.