Editorial: add note about updating destination

To avoid confusion when implementers overlook the step where destination is updated to the correct navigable container.

Fixes whatwg#11306 and fixes whatwg#8383.

Author: TimvdLippe

source

@@ -103441,7 +103441,8 @@ location.href = '#foo';</code></pre>
      client</span></dd>
 
      <dt><span data-x="concept-request-destination">destination</span></dt>
-     <dd>"<code data-x="">document</code>"</dd>
+     <dd>"<code data-x="">document</code>" <span class="note">The destination is updated below when
+     <var>navigable</var> has a <span data-x="nav-container">container</span>.</span></dd>
 
      <dt><span data-x="concept-request-credentials-mode">credentials mode</span></dt>
      <dd>"<code data-x="">include</code>"</dd>