add result of sample

suomesta · suomesta · commit 5df0bc418e92 · 2023-01-07T13:02:36.000+09:00
diff --git a/reference/string/basic_string/op_compare_3way.md b/reference/string/basic_string/op_compare_3way.md
@@ -65,6 +65,7 @@ int main()
 
 ### 出力
 ```
+equal
 ```
 
 ## 参照
