docs: add appstore link in readme (#4370)

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#### What type of PR is this?
/kind documentation

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#### What this PR does / why we need it:
在 Readme 中增加应用市场链接。

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```release-note
NONE
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README.md

@@ -46,7 +46,7 @@ docker run \
 
 ## 生态
 
-可访问 [awesome-halo](https://github.com/halo-sigs/awesome-halo) 查看已经适用于 Halo 2.x 的主题和插件，以及适用于 Halo
+可访问 [官方应用市场](https://halo.run/store/apps) 或 [awesome-halo 仓库](https://github.com/halo-sigs/awesome-halo) 查看已经适用于 Halo 2.x 的主题和插件，以及适用于 Halo
 1.x 的相关仓库。
 
 ## 许可证