docs: add note on GUID storage during export in SuperConverter

- Included a comment in the SuperConverter class to clarify that the GUID is stored in custom properties during export to prevent unnecessary XML modifications if the document is not saved. This enhances code readability and understanding of the export process.

Author: caio-pizzol

packages/super-editor/src/core/super-converter/SuperConverter.js

@@ -421,6 +421,8 @@ class SuperConverter {
     this.documentModified = true;
     this.documentHash = null; // Clear temporary hash
 
+    // Note: GUID is stored to custom properties during export to avoid
+    // unnecessary XML modifications if the document is never saved
     return this.documentGuid;
   }