Merge pull request #108 from curbengh/hexo-4

docs: recommend v2 to hexo v4

Author: curbengh

README.md

@@ -12,6 +12,7 @@ Generate Atom 1.0 or RSS 2.0 feed.
 $ npm install hexo-generator-feed --save
 ```
 
+- Hexo 4: 2.x
 - Hexo 3: 1.x
 - Hexo 2: 0.x