lib/mkNixpkgs.nix: Add function to import nixpkgs with overlays

lib/mkNixpkgs.nix

@@ -0,0 +1,27 @@
+{
+  inputs,
+  self,
+  ...
+}:
+
+/*
+
+  Loads a version of nixpkgs with nixfiles overlays loaded
+
+*/
+{
+  system,
+  nixpkgs ? inputs.nixpkgs,
+  overlays ? [],
+  ...
+}@args:
+
+import nixpkgs {
+  inherit system;
+  overlays = [
+    self.overlays.clerie-inputs
+    self.overlays.clerie-pkgs
+    self.overlays.clerie-build-support
+    self.overlays.clerie-overrides
+  ] ++ overlays;
+}