feat: add artplayer-plugin-jassub with initial implementation and documentation

docs/assets/example/jassub.js

@@ -0,0 +1,12 @@
+// npm i artplayer-plugin-jassub
+// import artplayerPluginJassub from 'artplayer-plugin-jassub';
+
+var art = new Artplayer({
+    container: '.artplayer-app',
+    url: '/assets/sample/video.mp4',
+    plugins: [
+        artplayerPluginJassub({
+            //
+        }),
+    ],
+});