chore(oas): add note about returned fields in list product variants endpoint (#5360)

packages/medusa/src/api/routes/admin/products/list-variants.ts

@@ -12,7 +12,10 @@ import { validator } from "../../../../utils/validator"
  * @oas [get] /admin/products/{id}/variants
  * operationId: "GetProductsProductVariants"
  * summary: "List a Product's Variants"
- * description: "Retrieve a list of Product Variants associated with a Product. The variants can be paginated."
+ * description: |
+ *   Retrieve a list of Product Variants associated with a Product. The variants can be paginated.
+ *
+ *   By default, each variant will only have the `id` and `variant_id` fields. You can use the `expand` and `fields` request parameters to retrieve more fields or relations.
  * x-authenticated: true
  * parameters:
  *   - (path) id=* {string} ID of the product.