自定义文章页头图

通过配置每篇文章(即.md文件)的头部的header_image字段来修改，如果不填写将采用主题配置中的post_header_image字段，如果post_header_image字段未填写则采用site_header_image字段。

By modifying the header_image property of the header of each article, if you do not fill in the post configuration, the post_header_image property in theme configuration will be used , if post_header_image is not filled, the site_header_image field will be used.

eg：

---
title: Tags
date: 2013-12-24 23:29:53
tags:
- Foo
- Bar
- Baz
header_image: /intro/post-bg.jpg
---