add git link to index.html

public/index.html

@@ -15,6 +15,9 @@
     <h3>HeroUnion联盟状态</h3>
     <pre><code id="herounion_stats">...</code></pre>
 
+    <h3>HeroUnion源码下载</h3>
+    <p><a href="https://git.filesite.io/filesite/hero_union" target="_blank">https://git.filesite.io/filesite/hero_union</a></p>
+
     <script type="text/javascript">
         var api = '/api/stats/';
         $.ajax({