Add darkkirb repository

This repository currently contains the following packages:

- Akkoma, and its pleroma and admin frontends, built from git, with
  patches for my personal instance
- matrix-media-repo built from git
- git versions of mautrix-signal and mautrix-telegram
- mautrix-discord and mautrix-whatsapp, also built from git
- a usually more updated version of papermc
- Plover with openstenoproject/plover#1461 (comment)
  applied (wayland support)
- a few plover plugins, latest pypi version
- KreativeKorp’s fonts
- Emoji for akkoma made by volpeon (https://volpeon.ink/)

repos.json

@@ -171,6 +171,10 @@
             "github-contact": "dali99",
             "url": "https://git.dodsorf.as/Dandellion/NUR"
         },
+        "darkkirb": {
+            "github-contact": "DarkKirb",
+            "url": "https://git.chir.rs/darkkirb/nix-packages"
+        },
         "dawidsowa": {
             "github-contact": "dawidsowa",
             "url": "https://github.com/dawidsowa/nur-packages"