Move upload source hint to be more noticeable

It's difficult to find when it only appears when hovering over the
Source label, but it's important information for uploaders to know.

app/assets/stylesheets/specific/uploads.css.scss

@@ -18,6 +18,10 @@ div#c-uploads {
       margin-bottom: 0.5em;
     }
 
+    .hint {
+      display: block;
+    }
+
     div#source-info {
       margin: 1em 0;
       padding: 1em;