feat: add description of db.transaction()

Author: limcheekin

example/lib/main.dart

@@ -221,14 +221,18 @@ class _HomePageState extends State<HomePage> {
       'db.delete()',
     );
 
-    await execute(() => db.transaction((txn) async {
-          txn.query('DEFINE TABLE test SCHEMAFULL;');
-          txn.query('DEFINE FIELD name ON test TYPE string;');
-          txn.query(
-            r'CREATE test SET name = $name;',
-            bindings: {'name': 'John'},
-          );
-        }));
+    await execute(
+        () => db.transaction(
+              (txn) async {
+                txn.query('DEFINE TABLE test SCHEMAFULL;');
+                txn.query('DEFINE FIELD name ON test TYPE string;');
+                txn.query(
+                  r'CREATE test SET name = $name;',
+                  bindings: {'name': 'John'},
+                );
+              },
+            ),
+        'db.transaction()');
   }
 
   @override