README.md: Mention kate as a Client

The `kate` editor has `yaml-language-server` as its default for the YAML format built-in (no plugins or manual configuration needed).

Author: nthykier

README.md

@@ -388,6 +388,7 @@ This repository only contains the server implementation. Here are some known cli
 - [Vim-EasyComplete](https://github.com/jayli/vim-easycomplete) for Vim/NeoVim
 - [nova-yaml](https://github.com/robb-j/nova-yaml/) for Nova
 - [volar-service-yaml](https://github.com/volarjs/services/tree/master/packages/yaml) for Volar
+- [Kate](https://kate-editor.org/)
 
 ## Developer Support