add README, conduit

modules/nixos/matrix-conduit.nix

@@ -0,0 +1,13 @@
+{config, ...}: {
+  services.matrix-conduit = {
+    enable = true;
+    settings.global = {
+      server_name = "${config.networking.domain}";
+      address = "localhost";
+      database_backend = "rocksdb";
+      allow_registration = true;
+      allow_federation = true;
+    };
+    secretFile = config.age.secrets.conduit-secretFile.path;
+  };
+}