feat: add inject support

Co-authored-by: st1020 <me@st1020.com>

README.md

@@ -12,6 +12,7 @@ This theme is based on Hugo theme [hugo-paper](https://github.com/nanxiaobei/hug
 
 - Easy to use and modify
 - No preset limits (This theme does not limit your content directory structure, taxonomy names, etc. It's applicable to all zola sites.)
+- Inject support
 - Dark mode
 - Responsive design
 - Social icons
@@ -49,6 +50,20 @@ theme = "kita"
 
 See the `extra` section in [config.toml](https://github.com/st1020/kita/blob/main/config.toml) as a example.
 
+## Inject support
+
+You can easily use inject to add new features to your side without modifying the theme itself.
+
+To use inject, you need to add some HTML files to the `templates/injects` directory.
+
+The available inject points are: `head`, `header_nav`, `body_start`, `body_end`, `page_start`, `page_end`, `footer`, `page_info`.
+
+For example, to load a custom script, you can add a `templates/injects/head.html` file:
+
+```html
+<script src="js-file-path-or-cdn-url.js"></script>
+```
+
 ## License
 
 [MIT License](https://github.com/st1020/kita/blob/main/LICENSE)