Updated logo and architecture links. (#2529)

Signed-off-by: NPahudPlus <haimeng.cai@zilliz.com>

README.md

-![Milvuslogo](https://github.com/milvus-io/docs/blob/master/assets/milvus_logo.png)
-
+![Milvuslogo](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_logo.png)
 [![Slack](https://img.shields.io/badge/Join-Slack-orange)](https://join.slack.com/t/milvusio/shared_invite/zt-e0u4qu3k-bI2GDNys3ZqX1YCJ9OM~GQ)
 ![GitHub](https://img.shields.io/github/license/milvus-io/milvus)
 ![Docker pulls](https://img.shields.io/docker/pulls/milvusdb/milvus)
@@ -19,8 +18,7 @@ As an open source vector similarity search engine, Milvus is easy-to-use, highly
 
 Milvus has the following architecture:
 
-![arch](https://github.com/milvus-io/docs/blob/v0.7.1/assets/milvus_arch.png)
-
+![arch](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_arch.png)
 For more detailed introduction of Milvus and its architecture, see [Milvus overview](https://www.milvus.io/docs/about_milvus/overview.md). Keep up-to-date with newest releases and latest updates by reading Milvus [release notes](https://www.milvus.io/docs/releases/release_notes.md).
 
 Milvus is an [LF AI Foundation](https://lfai.foundation/) incubation project. Learn more at [lfai.foundation](https://lfai.foundation/).

README_CN.md

-![Milvuslogo](https://github.com/milvus-io/docs/blob/master/assets/milvus_logo.png)
 
+![Milvuslogo](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_logo.png)
 [![Slack](https://img.shields.io/badge/Join-Slack-orange)](https://join.slack.com/t/milvusio/shared_invite/zt-e0u4qu3k-bI2GDNys3ZqX1YCJ9OM~GQ)
 
 ![GitHub](https://img.shields.io/github/license/milvus-io/milvus)
@@ -21,7 +21,7 @@ Milvus 是一款开源的特征向量相似度搜索引擎，具有使用方便
 
 Milvus 的架构如下：
 
-![arch](https://github.com/milvus-io/docs/raw/v0.7.1/assets/milvus_arch.png)
+![arch](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_arch.png)
 
 若要了解 Milvus 详细介绍和整体架构，请访问 [Milvus 简介](https://www.milvus.io/cn/docs/about_milvus/overview.md)。您可以通过 [版本发布说明](https://www.milvus.io/cn/docs/releases/release_notes.md) 获取最新版本的功能和更新。