This reverts commit 203dc39a for the README.

Perhaps we'll customize this further when I'll be inspired.

Implements #4

Also introduce a translations file for our "textbook" theme.

It is now submitted.

It's okay, PR is on the way.

(now I need to give it its own repository)
(and to translate it into french)

Notice that mathjax uses a CDN.
This is temporary.

This git tree is not going to be a bonzaï anytime soon.

(that was bound to happen sometime)
We're also adding two tentative CSS fixes for the theme and language-selector plugin.

A pretty dirty one, if you ask me.