docs: add reference TOC docs

docs/docs/table-of-contents.md

@@ -28,10 +28,6 @@ The YAML document is a tree of TOC nodes, each of which has these properties:
 - `uid`: The uid of the article. Can be used instead of `href`.
 - `expanded`: Expand children on load, only works if the template is `modern`.
 
-## Navigation Bar
-
-The `toc.yml` file in the `docfx.json` folder will be used to fill the content of the navigation bar at the top of the page.
-
 ## Nested TOCs
 
 To nest a TOC within another TOC, set the `href` property to point to the `toc.yml` file that you want to nest. You can also use this structure as a way to reuse a TOC structure in one or more TOC files.
@@ -66,3 +62,57 @@ Reference
 ├─ System.String
 ├─ System.Float
 ```
+
+## Reference TOCs
+
+To reference another TOC without embeding it to a parent TOC using nested TOCs, set the `href` property to point to the directory that you want to reference and end the string with `/`, this will generate a link pointing to the first article in the referenced TOC.
+
+Consider the following folder structure:
+
+```
+toc.yml
+├─ System
+    ├─ toc.yml
+├─ System.Collections
+    ├─ toc.yml
+```
+
+_toc.yml_:
+
+```yml
+- name: System
+  href: System/
+- name: System.Collections
+  href: System.Collections/
+```
+
+This structure renders as follows:
+
+
+```yml
+System # Link to the first article in System/toc.yml
+System.Collections  # Link to the first article in System.Collections/toc.yml
+```
+
+## Navigation Bar
+
+The `toc.yml` file in the `docfx.json` folder will be used to fill the content of the navigation bar at the top of the page. It usually uses [Reference TOCs](#reference-tocs) to navigate to child pages.
+
+The following example creates a navigation bar with two  _Docs_ and _API_ entries:
+
+```
+toc.yml
+├─ docs
+    ├─ toc.yml
+├─ api
+    ├─ toc.yml
+```
+
+_toc.yml_:
+
+```yml
+- name: Docs
+  href: docs/
+- name: API
+  href: api/
+```