Drop old channels from CI and fix README

.github/workflows/ci.yaml

@@ -107,22 +107,13 @@ jobs:
         os: [ubuntu-latest, macos-latest]
         rust-channel: [stable, beta, nightly]
         profile: [minimal, default]
-        nixpkgs-channel: [nixpkgs-unstable, nixos-21.11]
-        exclude:
-          - os: macos-latest
-            nixpkgs-channel: nixos-21.11
+        nixpkgs-channel: [nixpkgs-unstable, nixos-22.11]
         include:
           # The legacy package, used by compatible functions.
           - os: ubuntu-latest
             rust-channel: stable
             profile: rust
             nixpkgs-channel: nixpkgs-unstable
-          # Old Nix
-          - os: ubuntu-latest
-            rust-channel: stable
-            profile: default
-            nixpkgs-channel: nixos-21.11
-            nix_install_url: https://releases.nixos.org/nix/nix-2.4/install
 
     runs-on: ${{ matrix.os }}
     env:

README.md

@@ -13,12 +13,8 @@ no need to have network access. It also works well with [Nix Flakes](https://nix
 - Current oldest supported version is stable 1.29.0 and beta/nightly 2018-09-13
   (which are randomly picked and may change over time).
 
-rust-overlay is targeting these channels and they are tested on CI.
-Other channels may be supported but are not guarenteed.
-- nixpkgs-unstable
-- nixos-21.11 (for Linux)
-
-The minimal version of Nix supported is 2.4.
+rust-overlay targets nixos-unstable and supported releases of NixOS, on x86_64-linux.
+They are tested on CI. It may also work on other channels but is not guarenteed.
 
 For migration from [nixpkgs-mozilla], see [this section](#migration-from-nixpkgs-mozilla).
 
@@ -225,6 +221,10 @@ Running `nix develop` will create a shell with the default beta Rust toolchain i
 - [Reference of all public attributes](docs/reference.md)
 - [Cross compilation](docs/cross_compilation.md)
 
+## License
+
+MIT licensed.
+
 [nixpkgs-mozilla]: https://github.com/mozilla/nixpkgs-mozilla
 [rust-toolchain]: https://rust-lang.github.io/rustup/overrides.html#the-toolchain-file
 [rust-profiles]: https://rust-lang.github.io/rustup/concepts/profiles.html