Update front page

cn/css/main.css

@@ -331,3 +331,7 @@ body {
   margin-top: 5px;
   float: left;
   padding: 15px 15px; }
+
+.btn-pd {
+  margin-top: 5px;
+  margin-bottom: 5px; }

cn/index.html

@@ -80,9 +80,9 @@
             <h1>PaddlePaddle</h1>
             <hr>
 	    <p>开放易用的深度学习平台，工业应用与学术研究并举</p>
-	    <a href="http://www.paddlepaddle.org/doc_cn/demo/quick_start/index.html" class="btn btn-primary btn-xl page-scroll">快速上手</a>
-	    <a href="http://www.paddlepaddle.org/doc_cn/" class="btn btn-primary btn-xl page-scroll">文档</a>
-	    <a href="https://github.com/baidu/paddle" class="btn btn-primary btn-xl page-scroll">代码</a>
+	    <a href="http://www.paddlepaddle.org/doc_cn/demo/quick_start/index.html" class="btn btn-primary btn-xl page-scroll btn-pd">快速上手</a>
+	    <a href="http://www.paddlepaddle.org/doc_cn/" class="btn btn-primary btn-xl page-scroll btn-pd">文档</a>
+	    <a href="https://github.com/baidu/paddle" class="btn btn-primary btn-xl page-scroll btn-pd">代码</a>
         </div>
     </div>
 </header>

css/main.css

@@ -331,3 +331,7 @@ body {
   margin-top: 5px;
   float: left;
   padding: 15px 15px; }
+
+.btn-pd {
+  margin-top: 5px;
+  margin-bottom: 5px; }

index.html

@@ -80,9 +80,9 @@
             <h1>PaddlePaddle</h1>
             <hr>
 	    <p>Open and Easy-to-Use Deep Learning Platform for Enterprise and Research</p>
-	    <a href="http://paddlepaddle.org/doc/demo/quick_start/index_en.html" class="btn btn-primary btn-xl page-scroll">Quick Start</a>
-	    <a href="http://paddlepaddle.org/doc/" class="btn btn-primary btn-xl page-scroll">Documentation</a>
-	    <a href="https://github.com/baidu/paddle" class="btn btn-primary btn-xl page-scroll">Code</a>
+	    <a href="http://paddlepaddle.org/doc/demo/quick_start/index_en.html" class="btn btn-primary btn-xl page-scroll btn-pd">Quick Start</a>
+	    <a href="http://paddlepaddle.org/doc/" class="btn btn-primary btn-xl page-scroll btn-pd">Documentation</a>
+	    <a href="https://github.com/baidu/paddle" class="btn btn-primary btn-xl page-scroll btn-pd">Code</a>
         </div>
     </div>
 </header>
@@ -256,7 +256,7 @@
             <div class="col-lg-8 col-lg-offset-2 text-center">
                 <h2 class="section-heading">Let's Get In Touch!</h2>
                 <hr class="primary">
-                <p>If there is any problem to use PaddlePaddle, please contact paddle-dev@baidu.com</p>
+                <p>If you have any problems using PaddlePaddle, please contact paddle-dev@baidu.com.</p>
 	    </div>
 	</div>
     </div>