add documentation for different menu type

exampleSite/content/usage/menus.md

@@ -1,7 +1,30 @@
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-draft: true
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+The theme supports two different kinds of menus. [File-tree menu](#file-tree-menu) is the default one and does not require further configuration to work. If you want full control about your menu the [bundle menu](#bundle-menu) is a powerful option to accomplish it.
 
 ## File-tree menu
 
+As the name already suggests, the file tree menu builds a menu from the file system structure of the content folder. By default, areas and subareas are sorted alphabetically by the title of the pages. To manipulate the order the `weight` parameter in a page [front matter](https://gohugo.io/content-management/front-matter/) can be used. To structure your content folder you have to use [page bundles](https://gohugo.io/content-management/organization/#page-bundles), single files are **not** supported. Hugo will render build single files in the content folder just fine but it will not be added to the menu.
+
+**Example:**
+
+A file structure like shown below...
+
+```plain
+content/
+├── level-1
+│   ├── _index.md
+│   ├── level-1-1.md
+│   ├── level-1-2.md
+│   └── level-1-3
+│       ├── _index.md
+│       └── level-1-3-1.md
+└── level-2
+    ├── _index.md
+    ├── level-2-1.md
+    └── level-2-2.md
+```
+
+... results in a menu that looks like this.
+
+[![Example file-tree menu](/media/file-tree.png)](/media/file-tree.png)
+
 ## Bundle menu