fix: rename README_zn.md to README_zh.md for consistency (#919)

config_center/nacos/README_zh.md

diff --git a/config_center/nacos/README_zn.md b/config_center/nacos/README_zh.md
similarity index 100%
rename from config_center/nacos/README_zn.md
rename to config_center/nacos/README_zh.md

config_center/zookeeper/README_zh.md

diff --git a/config_center/zookeeper/README_zn.md b/config_center/zookeeper/README_zh.md
similarity index 100%
rename from config_center/zookeeper/README_zn.md
rename to config_center/zookeeper/README_zh.md

context/README_zh.md

diff --git a/context/README_zn.md b/context/README_zh.md
similarity index 100%
rename from context/README_zn.md
rename to context/README_zh.md

error/README_zh.md

diff --git a/error/README_zn.md b/error/README_zh.md
similarity index 100%
rename from error/README_zn.md
rename to error/README_zh.md