docs: restructure documentation

docs/manual/configuring/custom-plugins/new-method.md

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+# New Method {#sec-new-method}
+
+As of version **0.5**, we have a more extensive API for configuring plugins, under `vim.extraPlugins`.
+
+Instead of using DAGs exposed by the library, you may use the extra plugin module as follows:
+
+```nix
+{
+  config.vim.extraPlugins = with pkgs.vimPlugins; {
+    aerial = {
+      package = aerial-nvim;
+      setup = ''
+        require('aerial').setup {
+          -- some lua configuration here
+        }
+      '';
+    };
+
+    harpoon = {
+      package = harpoon;
+      setup = "require('harpoon').setup {}";
+      after = ["aerial"];
+    };
+  };
+}
+```