docs: highlight HTTP Cache support

Author: fengkx

README.md

@@ -15,6 +15,7 @@ Another telegram RSSBot in Node.js
 
 # Hightlights
 
+1. [HTTP Caching](https://tools.ietf.org/html/rfc7234#section-4.3.1)
 1. Import and export an opml file
 1. [Various configuration](https://rssbot.vercel.app/guide/configurations)
 1. Pagination on command that list feeds
@@ -31,6 +32,7 @@ Visit [rssbot.vercel.app](https://rssbot.vercel.app) to see full documentation.
 
 # Hightlights
 
+1. [HTTP Caching](https://tools.ietf.org/html/rfc7234#section-4.3.1)
 1. OPML 文件导入导出
 1. [丰富的可配置项](https://rssbot.vercel.app/zh/guide/configurations)
 1. 命令支持按键翻页