Update architecture diagram

Author: daixba

README.md

@@ -47,7 +47,7 @@ Please make sure you have met below prerequisites:
 
 The following diagram illustrates the reference architecture. Note that it also includes a new **VPC** with two public subnets only for the Application Load Balancer (ALB).
 
-![Architecture](assets/arch.svg)
+![Architecture](assets/arch.png)
 
 You can also choose to use [AWS Fargate](https://aws.amazon.com/fargate/) behind the ALB instead of [AWS Lambda](https://aws.amazon.com/lambda/), the main difference is the latency of the first byte for streaming response (Fargate is lower).
 

README_CN.md

@@ -49,7 +49,7 @@ OpenAI 的 API 或 SDK 无缝集成并试用 Amazon Bedrock 的模型,而无需
 
 下图展示了本方案的参考架构。请注意,它还包括一个新的**VPC**,其中只有两个公共子网用于应用程序负载均衡器(ALB)。
 
-![Architecture](assets/arch.svg)
+![Architecture](assets/arch.png)
 
 您也可以选择在 ALB 后面接 [AWS Fargate](https://aws.amazon.com/fargate/) 而不是 [AWS Lambda](https://aws.amazon.com/lambda/)，主要区别在于流响应的首字节延迟（Fargate更低）。