Improve docs for LogInterceptor

dio/README-ZH.md

@@ -475,6 +475,12 @@ print(response.data); // 'fake data'
 dio.interceptors.add(LogInterceptor(responseBody: false)); // 不输出响应内容体
 ```
 
+When using Flutter, you should use `debugPrint` to print logs:
+
+```dart
+dio.interceptors.add(LogInterceptor(logPrint: (o) => debugPrint(o.toString())));
+```
+
 **注意：** 由于拦截器队列是先进先出，`LogInterceptor` 应当在最后添加至 `Dio` 实例。
 
 **注意：** 日志默认仅在 DEBUG 模式（启用了断言）下打印。

dio/README.md

@@ -490,7 +490,14 @@ You can apply the `LogInterceptor` to log requests and responses automatically i
 dio.interceptors.add(LogInterceptor(responseBody: false)); // Do not output responses body.
 ```
 
-**Note:** `LogInterceptor` should be the last to add since the interceptors are FIFO.
+When using Flutter, you should use `debugPrint` to print logs:
+
+```dart
+dio.interceptors.add(LogInterceptor(logPrint: (o) => debugPrint(o.toString())));
+```
+
+**Note:** `LogInterceptor` should be the last interceptor added, otherwise modifications by following interceptors
+will not be logged.
 
 **Note:** Logs will only be printed in the DEBUG mode (when the assertion is enabled).
 

dio/lib/src/interceptors/log.dart

@@ -4,9 +4,18 @@ import '../options.dart';
 import '../response.dart';
 
 /// [LogInterceptor] is used to print logs during network requests.
-/// It's better to add [LogInterceptor] to the tail of the interceptor queue,
-/// otherwise the changes made in the interceptor behind A will not be printed out.
+/// [LogInterceptor] should be the last interceptor added,
+/// otherwise modifications by following interceptors will not be logged.
 /// This is because the execution of interceptors is in the order of addition.
+///
+/// **Note**
+/// When used in Flutter, make sure to use `debugPrint` to print logs.
+///
+/// ```dart
+/// dio.interceptors.add(LogInterceptor(
+///  logPrint: (o) => debugPrint(o.toString()),
+/// ));
+/// ```
 class LogInterceptor extends Interceptor {
   LogInterceptor({
     this.request = true,