Docs: update outdated guide to make code open by default

code/addons/docs/docs/docspage.md

@@ -165,10 +165,10 @@ You can override this default behavior in `.storybook/preview.js` (or in any of
 ```js
 export const parameters = {
   docs: {
-    source: {
-      state: 'open',
-    },
-  },
+    canvas: {
+      sourceState: 'shown'
+    }
+  }
 };
 ```