Docs: add balbel-plugin-import install guide

docs/src/ExamplesApp.vue

@@ -2,7 +2,7 @@
   <router-view></router-view>
 </template>
 
-<style>
+<style lang="postcss">
 body {
   -webkit-font-smoothing: antialiased;    
 }

docs/src/ExamplesDocsApp.vue

@@ -34,3 +34,11 @@ export default {
   }
 };
 </script>
+
+<style lang="postcss">
+.zan-doc-content--quickstart {
+  h3:not(:first-of-type) {
+    margin-top: 35px;
+  }
+}
+</style>