website: add alt-tags to images

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/header.html

@@ -47,7 +47,8 @@
               <li><a href="/contribute.html">Contribute</a></li>
               <li><a href="/sponsors.html">Sponsors</a></li>
             </ul>
-            <a class="gplus" href="https://plus.google.com/100084591154899263420/posts"><img src="images/gplus.png" height="28" width="28"></a>
+            <a class="gplus" href="https://plus.google.com/100084591154899263420/posts">
+            <img src="images/gplus.png" height="28" width="28" alt="Google+" /></a>
           </div><!--/.nav-collapse -->
         </div>
       </div>

docs/index.html

@@ -2,7 +2,8 @@
 
 <div class="hero-unit">
   <div class="row-fluid">
-    <img src="images/logo.png" height="170" width="170" style="float: right;"/>
+    <img src="images/logo.png" height="170" width="170" style="float: right;"
+        alt="Buildroot logo" />
     <div class="span8">
       <h1>Buildroot<br/><small>Making Embedded Linux Easy</small></h1>
       <p>Buildroot is a simple, efficient and easy-to-use tool to generate