feat: add social preview image

Author: PSDat123

_config.yml

@@ -80,7 +80,7 @@ avatar: ./assets/img/avatar.jpeg
 
 # The URL of the site-wide social preview image used in SEO `og:image` meta tag.
 # It can be overridden by a customized `page.image` in front matter.
-social_preview_image: # string, local or CORS resources
+social_preview_image: /assets/img/preview.png # string, local or CORS resources
 
 # boolean type, the global switch for TOC in posts.
 toc: true