Update copy for download link for travel advice map

FCDO would like the copy of this link updated to be more specific.
Zendesk ticket: https://govuk.zendesk.com/agent/tickets/5495177

app/views/shared/_travel_advice_first_part.html.erb

@@ -4,7 +4,7 @@
     <img src="<%= content_item.map["url"] %>" alt="<%= content_item.map["alt_text"] %>" class="map-image">
     <% if content_item.map_download_url %>
       <figcaption>
-        <%= render 'components/download_link', href: content_item.map_download_url, link_text: "Download map (PDF)" %>
+        <%= render 'components/download_link', href: content_item.map_download_url, link_text: "Download a more detailed map (PDF)" %>
       </figcaption>
     <% end %>
   </figure>