nix: nixify the setup, add prettier

nix/sources.json

@@ -0,0 +1,38 @@
+{
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "5830a4dd348d77e39a0f3c4c762ff2663b602d4c",
+        "sha256": "1d3lsrqvci4qz2hwjrcnd8h5vfkg8aypq3sjd4g3izbc8frwz5sm",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/5830a4dd348d77e39a0f3c4c762ff2663b602d4c.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "master",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "21.05",
+        "sha256": "1ckzhh24mgz6jd1xhfgx0i9mijk6xjqxwsshnvq789xsavrmsc36",
+        "type": "tarball",
+        "url": "https://github.com/nixos/nixpkgs/archive/21.05.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "npmlock2nix": {
+        "branch": "master",
+        "description": null,
+        "homepage": null,
+        "owner": "nix-community",
+        "repo": "npmlock2nix",
+        "rev": "ff17a3c59233911f776d8d462d61d82a3e41df34",
+        "sha256": "0l624gkkpn1r0g48b204k0wcqm9cwy5rzd5mnxwfjhyjj1wg4nl7",
+        "type": "tarball",
+        "url": "https://github.com/nix-community/npmlock2nix/archive/ff17a3c59233911f776d8d462d61d82a3e41df34.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}