chore: editor-standalone link in README

Author: Picalines

README.md

@@ -8,6 +8,8 @@
 </p>
 
 <p align="center">
+  <a href="https://picalines.github.io/kepvox/editor/" style="text-decoration: none">
+    <img alt="standalone editor" src="https://img.shields.io/badge/standalone_editor-black?style=for-the-badge&logo=github&link=https%3A%2F%2Fpicalines.github.io%2Fkepvox%2Feditor"></a>
   <a href="https://picalines.github.io/kepvox/synth-playground/" style="text-decoration: none">
     <img alt="synth package playground" src="https://img.shields.io/badge/synth_package_playground-black?style=for-the-badge&logo=github&link=https%3A%2F%2Fpicalines.github.io%2Fkepvox%2Fsynth-playground"></a>
 </p>