docs: add coverage badge

Author: hunterliu1003

docs/content/zh-Hant/index.md

@@ -33,6 +33,7 @@ features:
   <a href="https://www.npmjs.com/package/vue-final-modal">
     <img src="https://badgen.net/badgesize/brotli/hunterliu1003/vue-final-modal/master/dist/VueFinalModal.umd.js" alt="Size">
   </a>
+  <a href='https://coveralls.io/github/vue-final/vue-final-modal?branch=master'><img src='https://coveralls.io/repos/github/vue-final/vue-final-modal/badge.svg?branch=master' alt='Coverage Status' /></a>
 </p>
 
 <p class="flex h-8 space-x-4">
@@ -42,6 +43,7 @@ features:
   <a href="https://www.npmjs.com/package/vue-final-modal">
     <img src="https://badgen.net/badgesize/brotli/hunterliu1003/vue-final-modal/v3/dist/VueFinalModal.umd.js" alt="Size">
   </a>
+  <a href='https://coveralls.io/github/vue-final/vue-final-modal?branch=v3'><img src='https://coveralls.io/repos/github/vue-final/vue-final-modal/badge.svg?branch=v3' alt='Coverage Status' /></a>
 </p>
 
 <p align="right">