bingo: optional prose per datacenter page

The datacenter pages carry only generated sentences, which is thin
content to rank on. Migration 015 adds about_ru/en/uk, edited in the
admin form and rendered as paragraphs below the facts.

There is deliberately no fallback to ru: Russian prose on the English
page would hurt more than an absent paragraph.

Assisted-by: Claude:opus-5

views/bingo/dc.erb

@@ -14,6 +14,7 @@
     <h1><%= dc.l(:name, @locale) %></h1>
     <%== erb :_dc_meta, layout: false, locals: { dc: dc } %>
     <p class="facts"><%= dc_facts(dc).join(' ') %></p>
+    <% dc.about(@locale).each do |para| %><p class="facts"><%= para %></p><% end %>
     <section>
       <h2><%= t(:incidents) %></h2>
       <%== erb :_dc_incidents, layout: false, locals: { dc: dc } %>