docs: update README.md

README.md

 <div align="center">
 
-<img src="https://static.requarks.io/logo/wikijs-full.svg" alt="Wiki.js" width="600" />
+<img src="https://static.requarks.io/logo/wikijs-full.svg#gh-light-mode-only" alt="Wiki.js" width="600" /><img src="https://static.requarks.io/logo/wikijs-full-darktheme.svg#gh-dark-mode-only" alt="Wiki.js" width="600" />
 
 [![Release](https://img.shields.io/github/release/Requarks/wiki.svg?style=flat&maxAge=3600)](https://github.com/Requarks/wiki/releases)
 [![License](https://img.shields.io/badge/license-AGPLv3-blue.svg?style=flat)](https://github.com/requarks/wiki/blob/master/LICENSE)