Add documentation for docs multi-instance support

website/docs/guides/docs/docs-multi-instance.mdx

@@ -5,7 +5,7 @@ description: Use multiple docs plugin instances on a single Docusaurus site.
 slug: /docs-multi-instance
 ---
 
-The `@docusaurus/plugin-content-docs` plugin can support [multi-instance](../../using-plugins#multi-instance-plugins-and-plugin-ids).
+The `@docusaurus/plugin-content-docs` plugin can support [multi-instance](../../using-plugins.md#multi-instance-plugins-and-plugin-ids).
 
 :::note
 

website/docs/using-plugins.md

@@ -78,11 +78,13 @@ module.exports = {
 
 ## Multi-instance plugins and plugin ids
 
-It is possible to use multiple times the same plugin, on the same Docusaurus website.
+All Docusaurus content plugins can support multiple plugin instances.
 
-In this case, it is required to assign a unique id to each plugin instance.
+The Docs plugin has [additional multi-instance documentation](./guides/docs/docs-multi-instance.mdx)
 
-By default, the plugin id is `default`. At most one plugin can omit the id and use this default value.
+It is required to assign a unique id to each plugin instance.
+
+By default, the plugin id is `default`.
 
 ```js {6,13} title="docusaurus.config.js"
 module.exports = {
@@ -105,6 +107,12 @@ module.exports = {
 };
 ```
 
+:::note
+
+At most one plugin instance can be the "default plugin instance", by omitting the `id` attribute, or using `id: 'default'`.
+
+:::
+
 ## Plugins design
 
 Docusaurus' implementation of the plugins system provides us with a convenient way to hook into the website's lifecycle to modify what goes on during development/build, which involves (but not limited to) extending the webpack config, modifying the data being loaded and creating new components to be used in a page.