docs: update image size in readme

Author: kevwan

readme-cn.md

@@ -36,7 +36,7 @@
 
 以上实际都是在进行对输入数据进行处理最后输出清洗后的数据，针对数据处理有个非常经典的异步模式：生产者消费者模式。于是我们可以抽象一下数据批处理的生命周期，大致可以分为三个阶段：
 
-![](https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-serial-cn.png)
+<img src="https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-serial-cn.png" width="500">
 
 1. 数据生产 generate
 2. 数据加工 mapper
@@ -46,7 +46,7 @@
 
 再来思考一下不同阶段之间数据应该如何流转，既然不同阶段的数据处理都是由不同 goroutine 执行的，那么很自然的可以考虑采用 channel 来实现 goroutine 之间的通信。
 
-![](https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-cn.png)
+<img src="https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-cn.png" width="500">
 
 
 如何实现随时终止流程呢？

readme.md

@@ -23,7 +23,7 @@ Let's try to put ourselves in the author's shoes and sort out the possible busin
 
 The above is actually processing the input data and finally outputting the cleaned data. There is a very classic asynchronous pattern for data processing: the producer-consumer pattern. So we can abstract the life cycle of data batch processing, which can be roughly divided into three phases.
 
-![](https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-serial-en.png)
+<img src="https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-serial-en.png" width="500">
 
 1. data production generate
 2. data processing mapper
@@ -33,7 +33,7 @@ Data producing is an indispensable stage, data processing and data aggregation a
 
 Since different stages of data processing are performed by different goroutines, it is natural to consider the use of channel to achieve communication between goroutines.
 
-![](https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-en.png)
+<img src="https://raw.githubusercontent.com/zeromicro/zero-doc/main/doc/images/mapreduce-en.png" width="500">
 
 How can I terminate the process at any time?