Create page: add related topics section (#2149)

* Create page: add related topics section

- as defined in https://github.com/home-assistant/home-assistant.io/pull/32372
- add usage example

* Add info that title is optional

* Update docs/documenting/create-page.md

Co-authored-by: Joakim Sørensen <joasoe@gmail.com>

---------

Co-authored-by: Joakim Sørensen <joasoe@gmail.com>

docs/documenting/create-page.md

@@ -20,6 +20,11 @@ ha_config_flow: true
 ha_codeowners:
   - '@balloob'
 ha_domain: awesome
+related:
+  - docs: /voice_control/s3_box_voice_assistant/
+    title: Creating a ESP32-S3-BOX-3 voice assistant
+  - url: https://esphome.io/projects/index.html
+    title: ESPHome projects website
 ---
 
 Content... Written in markdown.
@@ -38,6 +43,7 @@ Additional keys for the file header:
 - `ha_config_flow`: Set to `true` if the integration has a [Data Entry Flow](/data_entry_flow_index.md), omit otherwise.
 - `ha_codeowners`: GitHub usernames or team names (starting with `@`) of people that are responsible for this integration. This should match with the codeowners as listed in the integration manifest file.
 - `ha_domain`: The domain of the integration in Home Assistant Core. This must match the name from the integration manifest file.
+- `related`: Optional. Adds a section with links to related topics to the end of the page. Use `docs` used for local links and `url` for external links. When using `docs`, the title key is optional. If not set, the title of the page you point to will be used.
 
 There are [pre-defined variables](https://jekyllrb.com/docs/variables/) available but usually, it's not necessary to use them when writing documentation.