Add missing default.nix for coqPackages.equations

pkgs/development/coq-modules/equations/default.nix

@@ -0,0 +1,45 @@
+{ stdenv, fetchFromGitHub, coq }:
+
+let param =
+  {
+    "8.6" = {
+      version = "1.0-beta";
+      rev = "v1.0-beta";
+      sha256 = "00pzlh5ij7s2hmpvimq1hjq3fjf0nrk997l3dl51kigx5r5dnvxd";
+    };
+
+    "8.7" = {
+      version = "cdf8c53";
+      rev = "cdf8c53f1f2274b29506f53bff476409ce717dc5";
+      sha256 = "0ipjzmviwnp0ippbkn03ld4j4j0dkzmyidmj4dvpdvymrkv31ai1";
+    };
+
+  }."${coq.coq-version}"
+; in
+
+stdenv.mkDerivation rec {
+
+  name = "coq${coq.coq-version}-equations-${version}";
+  version = "${param.version}";
+
+  src = fetchFromGitHub {
+    owner = "mattam82";
+    repo = "Coq-Equations";
+    rev = "${param.rev}";
+    sha256 = "${param.sha256}";
+  };
+
+  buildInputs = [ coq.ocaml coq.camlp5 coq.findlib coq ];
+
+  preBuild = "coq_makefile -f _CoqProject -o Makefile";
+
+  installFlags = "COQLIB=$(out)/lib/coq/${coq.coq-version}/";
+
+  meta = with stdenv.lib; {
+    homepage = https://mattam82.github.io/Coq-Equations/;
+    description = "A plugin for Coq to add dependent pattern-matching";
+    maintainers = with maintainers; [ jwiegley ];
+    platforms = coq.meta.platforms;
+  };
+
+}