add git fetch to migration instructions

Jacky Zhao

2023-08-20 90d6c1ed24283d0b046ba7eee2e6533a73cf3683

 content/index.md

@@ -13,7 +13,7 @@
```shell
git clone https://github.com/jackyzha0/quartz.git
cd quartz
git checkout v4-alpha
git checkout v4
npm i
npx quartz create
```