readme: add Discord chat badge (#5546)

README.md

@@ -2,14 +2,15 @@
   <a href="https://svelte.dev">
 	<img alt="Cybernetically enhanced web apps: Svelte" src="https://sveltejs.github.io/assets/banner.png">
   </a>
-
   <a href="https://www.npmjs.com/package/svelte">
     <img src="https://img.shields.io/npm/v/svelte.svg" alt="npm version">
   </a>
-
   <a href="https://github.com/sveltejs/svelte/blob/master/LICENSE">
     <img src="https://img.shields.io/npm/l/svelte.svg" alt="license">
   </a>
+  <a href="https://svelte.dev/chat">
+    <img src="https://img.shields.io/badge/chat-on%20discord-7289da.svg" alt="Chat">
+  </a>
 </p>