hint that relevance can be string

Author: andreer

en/reference/querying/default-result-format.html

@@ -364,7 +364,7 @@
 	  <p id="relevance">Double value representing the rank score.
       The rank score is returned from the <a href="../../ranking/ranking-intro.html">rank-profile</a>.
       See the <a href="../../learn/faq.html#what-could-cause-the-relevance-field-to-be--infinity">FAQ</a>
-      for how to handle <code>-Infinity</code> values.
+      for how to handle <code>"-Infinity"</code> (represented as string) values.
 	  </p>
 	</td>
   </tr>