Update index.html from @dlongley suggestion.

Co-Authored-By: Dave Longley <[email protected]>

Author: gkellogg

index.html

@@ -1274,7 +1274,8 @@ <h3>Algorithm</h3>
                   and <span class="changed">a copy of</span> <var>remote contexts</var>.
                   <div class="note">If <var>context</var> was previously dereferenced,
                     <a>processors</a> MUST make provisions for retaining the <var>base URL</var>
-                    of that <a>context</a> for this step.</div>
+                    of that <a>context</a> for this step to enable the resolution of any
+                    relative context URLs that may be encountered during processing.</div>
                 </li>
                 <li>Continue with the next <var>context</var>.</li>
               </ol>