[Miso] Adds Miso cache to Vega

system/hosts/vega/cachix/haskell-miso-cachix.nix

@@ -0,0 +1,13 @@
+
+{
+  nix = {
+    settings = {
+      substituters = [
+        "https://haskell-miso-cachix.cachix.org"
+      ];
+      trusted-public-keys = [
+        "haskell-miso-cachix.cachix.org-1:m8hN1cvFMJtYib4tj+06xkKt5ABMSGfe8W7s40x1kQ0="
+      ];
+    };
+  };
+}