Add padding around repository readme content

It looks quite bad without padding.

src/main/twirl/repo/files.scala.html

@@ -75,9 +75,9 @@
   </div>
   
   @readme.map { content =>
-  <div class="box">
+  <div id="readme" class="box">
     <div class="box-header">README.md</div>
     <div class="box-content">@markdown(content, repository, false, false)</div>
   </div>
   }
-}
+}