add sponsors to docs

Author: kazupon

README.md

@@ -5,13 +5,82 @@
 [![npm](https://img.shields.io/npm/v/@intlify/vue-i18n-extensions.svg)](https://www.npmjs.com/package/@intlify/vue-i18n-extensions)
 [![vue-i18n-extensions Dev Token](https://badge.devtoken.rocks/vue-i18n-extensions)](https://devtoken.rocks/package/vue-i18n-extensions)
 
-> Extensions for vue-i18n
+Extensions for vue-i18n
+
+## :warning: Notice
+This `next` branch is development branch for Vue 3! The version for Vue 2 is now in [`master`](https://github.com/intlify/vue-i18n-extensions/tree/master) branch!
+
+
+<h2 align="center">🤝 Supporting Intlify Project</h2>
+
+Intlify Project is an open source project that is included Vue I18n and i18n tooling and libralies with its ongoing development made possible entirely by the support of Sponsors. If you would like to become a sponsor, please consider:
+
+<p align="center">
+  <a
+    href="https://github.com/sponsors/kazupon"
+    target="_blank">
+    Become a Sponsor on GitHub
+  </a>
+</p>
+
+<h3 align="center">🥇 Gold Sponsors</h3>
+
+<p align="center">
+  <a
+    href="https://nuxtjs.org/"
+    target="_blank">
+    <img
+      src="https://raw.githubusercontent.com/intlify/vue-i18n-next/master/docs/public/nuxt.png"
+      width="240px"
+    />
+  </a>
+</p>
+
+<h3 align="center">🥈 Silver Sponsors</h3>
+
+<p align="center">
+  <a
+    href="https://www.codeandweb.com/babeledit?utm_campaign=vue-i18n-2019-01" 
+    target="_blank">
+    <img
+      src="https://secure.codeandweb.com/static/babeledit.svg"
+      width="200px"
+    />
+  </a>
+</p>
+
+<h3 align="center">🥉 Bronze Sponsors</h3>
+
+<p align="center">
+  <a href="https://zenarchitects.co.jp/" target="_blank">
+    <img
+      src="https://raw.githubusercontent.com/intlify/vue-i18n-next/master/docs/public/zenarchitects.png"
+      width="144px"
+    />
+  </a>
+</p>
+<p align="center">
+  <a href="https://www.sendcloud.com/" target="_blank">
+    <img
+      src="https://raw.githubusercontent.com/intlify/vue-i18n-next/master/docs/public/sendcloud.png"
+      width="144px"
+    />
+  </a>
+</p>
+<p align="center">
+  <a href="https://www.vuemastery.com/" target="_blank">
+    <img
+      src="https://raw.githubusercontent.com/intlify/vue-i18n-next/master/docs/public/vuemastery.png"
+      width="144px"
+    />
+  </a>
+</p>
+
+<br/>
 
-**NOTE:** :warning: This `next` branch is development branch for Vue 3! The version for Vue 2 is now in [`master`](https://github.com/intlify/vue-i18n-extensions/tree/master) branch!
 
 This library exports the following extensions:
 
-
 ## :star: Features
 
 - Server-side rendering for `v-t` custom directive