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;

app/views/uploads/new.html.erb

@@ -32,10 +32,11 @@
       </div>
 
       <div class="input">
-        <%= f.label :source, nil, :title => "You can enter a URL to have #{Danbooru.config.app_name} automatically download and process it" %>
+        <%= f.label :source %>
         <%= f.text_field :source, :size => 50, :value => params[:url] %>
         <%= button_tag "Similar", :id => "similar-button", :type => "button" %>
         <%= button_tag "Artist", :id => "find-artist-button", :type => "button" %>
+        <span class="hint">You can enter a URL to have <%= Danbooru.config.app_name %> automatically download and process it</span>
       </div>
 
       <div class="input">