fix typo (#1481)

Author: zhouzaida

README.md

@@ -24,9 +24,9 @@
 [![open issues](https://isitmaintained.com/badge/open/open-mmlab/mmengine.svg)](https://github.com/open-mmlab/mmengine/issues)
 [![issue resolution](https://isitmaintained.com/badge/resolution/open-mmlab/mmengine.svg)](https://github.com/open-mmlab/mmengine/issues)
 
-[Introduction](#introduction)
-[Installation](#installation)
-[Get Started](#get-started)
+[Introduction](#introduction) |
+[Installation](#installation) |
+[Get Started](#get-started) |
 [📘Documentation](https://mmengine.readthedocs.io/en/latest/) |
 [🤔Reporting Issues](https://github.com/open-mmlab/mmengine/issues/new/choose)