[Doc] Introduce 1.x in readme (#2025)

* introduce 1.x

* update

Author: xiexinch

README.md

@@ -82,6 +82,16 @@ v0.27.0 was released in 7/28/2022:
 
 Please refer to [changelog.md](docs/en/changelog.md) for details and release history.
 
+### 🌟 Preview of 1.x version
+
+A brand new version of **MMSegmentation v1.0.0rc0** was released in 31/8/2022:
+
+- Unifies interfaces of all components based on [MMEngine](https://github.com/open-mmlab/mmengine).
+- Faster training and testing speed with complete support of mixed precision training.
+- Refactored and more flexible [architecture](https://mmsegmentation.readthedocs.io/en/1.x/overview.html).
+
+Find more new features in [1.x branch](https://github.com/open-mmlab/mmsegmentation/tree/1.x). Issues and PRs are welcome!
+
 ## Installation
 
 Please refer to [get_started.md](docs/en/get_started.md#installation) for installation and [dataset_prepare.md](docs/en/dataset_prepare.md#prepare-datasets) for dataset preparation.

README_zh-CN.md

@@ -79,6 +79,16 @@ MMSegmentation 是一个基于 PyTorch 的语义分割开源工具箱。它是 O
 
 如果想了解更多版本更新细节和历史信息，请阅读[更新日志](docs/en/changelog.md)。
 
+### 🌟 1.x 预览版本
+
+全新的 **MMSegmentation v1.0.0rc0** 版本已经在 2022.8.31 发布：
+
+- 基于 [MMEngine](https://github.com/open-mmlab/mmengine) 统一了各组件接口。
+- 全面支持混合精度，训练测试速度更快。
+- 重构之后更加灵活的[架构](https://mmsegmentation.readthedocs.io/en/1.x/overview.html)。
+
+欢迎在 [1.x branch](https://github.com/open-mmlab/mmsegmentation/tree/1.x) 发现更多的新特性。欢迎 issue 和 PR。
+
 ## 安装
 
 请参考[快速入门文档](docs/zh_cn/get_started.md#installation)进行安装，参考[数据集准备](docs/zh_cn/dataset_prepare.md)处理数据。