Cleans up ui navigation

bookwyrm/templates/get_started/book_preview.html

@@ -4,7 +4,7 @@
     <label class="label" for="id_shelve_{{ book.id }}">
     <div class="select is-small">
         <select name="{{ book.id }}" aria-label="{% blocktrans with book_title=book.title %}Have you read {{ book_title }}?{% endblocktrans %}">
-            <option value="">-</option>
+            <option disabled selected value>Add to your books</option>
             {% for shelf in request.user.shelf_set.all %}
             <option value="{{ shelf.id }}">{{ shelf.name }}</option>
             {% endfor %}