add source for the now-current nixos release

nix/sources.json

@@ -41,6 +41,18 @@
         "url": "https://releases.nixos.org/nixos/21.05/nixos-21.05.3740.ce7a1190a0f/nixexprs.tar.xz",
         "url_template": "https://releases.nixos.org/nixos/21.05/nixos-21.05.3740.ce7a1190a0f/nixexprs.tar.xz"
     },
+    "release2111": {
+        "branch": "21.11",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a7ecde854aee5c4c7cd6177f54a99d2c1ff28a31",
+        "sha256": "162dywda2dvfj1248afxc45kcrg83appjd0nmdb541hl7rnncf02",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/a7ecde854aee5c4c7cd6177f54a99d2c1ff28a31.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "tahoe-lafs": {
         "branch": "master",
         "description": "The Tahoe-LAFS decentralized secure filesystem.",