zsh-completions: init at version 0.18.0 (#16512)

"This projects aims at gathering/developing new completion scripts that
are not available in Zsh yet. The scripts are meant to be contributed to
the Zsh project when stable enough."

pkgs/shells/zsh-completions/default.nix

@@ -0,0 +1,26 @@
+{ stdenv, fetchFromGitHub}:
+
+stdenv.mkDerivation rec {
+  name = "zsh-completions-${version}";
+  version = "0.18.0";
+
+  src = fetchFromGitHub {
+    owner = "zsh-users";
+    repo = "zsh-completions";
+    rev = "${version}";
+    sha256 = "0iwb1kaidjxaz66kbbdzbydbdlfc6dk21sflzar0zy25jgx1p4xs";
+  };
+
+  installPhase= ''
+    install -D --target-directory=$out/share/zsh/site-functions src/*
+  '';
+
+  meta = {
+    description = "Additional completion definitions for zsh";
+    homepage = "https://github.com/zsh-users/zsh-completions";
+    license = stdenv.lib.licenses.free;
+
+    platforms = stdenv.lib.platforms.unix;
+    maintainers = [ stdenv.lib.maintainers.olejorgenb ];
+  };
+}