Restyle README section

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/sections/tree.scss

@@ -113,3 +113,14 @@
   float: left;
   margin-top: 5px;
 }
+
+.readme-holder {
+  border-top: 1px dashed #CCC;
+  padding-top: 10px;
+
+  h4 {
+    font-size: 14px;
+    margin-bottom: 20px;
+    color: #777;
+  }
+}

app/views/projects/tree/_readme.html.haml

-.file-holder#README
-  .file-title
+.readme-holder#README
+  %h4
     %i.icon-file
       = readme.name
-  .file-content.wiki
+  .wiki
     - if gitlab_markdown?(readme.name)
       = preserve do
         = markdown(readme.data)