New features: asciidoc, fzf and spaceship;

[braun-daniel]

What type of PR is this?

• Add a new dev container collection
• Update to an existing dev container collection
• Documentation/spec update
• Other containers.dev site update (UX, layout, etc)

Related Issues

• Related Issue #
• Closes #

Description

Will introduce 3 new features:

• Asciidoctor: A fast text processor & publishing toolchain for converting AsciiDoc to HTML5, DocBook & more. Installed via. Ruby GEM.
• fzf: A general-purpose command-line fuzzy finder. Installed via. GIT.
• spaceship-prompt: A ZSH-prompt. Installed via. GIT.

Collection checklist

If your PR contributes a new collection, please utilize this checklist:

• Collection name
• Maintainer name
• Maintainer contact link (i.e. link to a GitHub repo, email)
• Repository URL
• OCI Reference
• I acknowledge that this collection provides new functionality, distinct from the existing collections part of this index.