Merge pull request #10826 from twbs/doc-multiple-navbars-unsupported

document that multiple navbars aren't supported by default

components.html

@@ -1416,6 +1416,10 @@ base_url: "../"
       <h4>Customize the collapsing point</h4>
       <p>Depending on the content in your navbar, you might need to change the point at which your navbar switches between collapsed and horizontal mode. Customize the <code>@grid-float-breakpoint</code> variable or add your own media query.</p>
     </div>
+    <div class="bs-callout bs-callout-warning" id="multiple-navbars-warning">
+      <h4>Multiple navbars require custom code</h4>
+      <p>Multiple nearby navbars with dropdown menus are not supported by default. You will need to override the <code>z-index</code>es of the dropdown menus yourself. Otherwise, the dropdown menu will display behind the other navbar.</p>
+    </div>
 
     <div class="bs-example">
       <nav class="navbar navbar-default" role="navigation">