Add notice for site closure (#65)

Author: takezoe

index.html

@@ -5,6 +5,13 @@
 <div class="home">
 
   <h1 class="page-heading">This is the community site for all the public <a href="https://github.com/gitbucket/gitbucket">GitBucket</a> plugins.</h1>
+
+  <strong>
+    Note: This site is no longer maintained and will soon be deleted completely.
+    The list of community plugins is now managed on a Wiki page in the gitbucket repository.<br/>
+    <a href="https://github.com/gitbucket/gitbucket/wiki/Community-Plugins">https://github.com/gitbucket/gitbucket/wiki/Community-Plugins</a>
+  </strong>
+
   <h1 class="page-heading">Available Plugins:</h1>
   <p class="separator"/>
   <ul class="plugin-list">