Add description to use default storage option hook

client/my-sites/plans-grid/hooks/npm-ready/data-store/use-default-storage-option.ts

@@ -6,13 +6,19 @@ type Props = {
 	storageOptions?: StorageOption[];
 };
 
+/**
+ * Returns the storage add-on upsell option to display to
+ * the user on initial load. If the user has purchased a
+ * storage add-on, that will be the default. Otherwise,
+ * the storage included with any given plan will be used.
+ *
+ */
 export default function useDefaultStorageOption( { storageOptions, storageAddOnsForPlan }: Props ) {
 	const [ purchasedStorageAddOnSlug ]: [ WPComStorageAddOnSlug ] =
 		( storageAddOnsForPlan?.find( ( storageAddOn ) => storageAddOn?.purchased )?.featureSlugs as [
 			WPComStorageAddOnSlug,
 		] ) ?? [];
 
-	// Default to most recently purchased storage add-on. Otherwise use default storage for plan.
 	return (
 		purchasedStorageAddOnSlug ||
 		storageOptions?.find( ( storageOption ) => ! storageOption.isAddOn )?.slug