Casper is not the default theme anymore

[tmlmt]

It is now Source, cf

Casper/README.md

Line 3 in 36e886a

The default theme for [Ghost](http://github.com/tryghost/ghost/). This is the latest development version of Casper! If you're just looking to download the latest release, head over to the [releases](https://github.com/TryGhost/Casper/releases) page.

The README file could point to this article for instance: https://ghost.org/tutorials/build-with-ghost-meet-our-new-official-theme/#meet-source-ghosts-new-default-theme

Casper is still maintained for the moment as a legacy theme used by many. It also lives in 2.8k forks including mine (see fantome) where I extended it with a few features (table of contents, locales, social media icons, etc.)