kubenix.submodule example used to create resources in multiple namespaces (#22)

docs/content/examples/namespaces/module.nix

@@ -0,0 +1,64 @@
+{
+  config,
+  lib,
+  pkgs,
+  kubenix,
+  ...
+}: {
+  imports = with kubenix.modules; [submodules k8s];
+
+  # Import submodule.
+  submodules.imports = [
+    ./namespaced.nix
+  ];
+
+  # We can now create multiple submodule instances.
+  submodules.instances.namespace-http = {
+    #                  ~~~~~~~~~~~~~~
+    #                          ^
+    #  ╭-----------------------╯
+    # The submodule instance name is injected as the name attribute to
+    # the submodule function. In this example, it is used as the namespace
+    # name.
+    #
+    # This needs to match config.submodule.name of an imported submodule.
+    submodule = "namespaced";
+    # Now we can set the args options defined in the submodule.
+    args.kubernetes.resources = {
+      services.nginx.spec = {
+        ports = [
+          {
+            name = "http";
+            port = 80;
+          }
+        ];
+        selector.app = "nginx";
+      };
+    };
+  };
+
+  submodules.instances.namespace-https = {
+    submodule = "namespaced";
+    args.kubernetes.resources = {
+      services.nginx.spec = {
+        ports = [
+          {
+            name = "https";
+            port = 443;
+          }
+        ];
+        selector.app = "nginx";
+      };
+    };
+    # Example of how other defaults can be applied to resources
+    # within a submodule.
+    args.kubernetes.version = "1.26";
+  };
+
+  # Resources defined in parent context use namespace set at this
+  # level and are not affected by the above submodules.
+  kubernetes.namespace = "default";
+  kubernetes.resources.services.nginx.spec = {
+    selector.app = "nginx-default";
+  };
+}