Extension - Docs - Add a note where user cannot override newtab incognito windows.

chrome/common/extensions/docs/static/override.html

 <style>
 #pics {
   margin:2em 1em 1.5em;
 }
 
 #pics td {
   text-align:center;
   width:50%!important;
   border:none;
   padding:0 1em;
@@ skipping 52 matching lines @@
 only one page.
 </p>
 
 <p class="note">
 <b>Note:</b>
 If you want to override the page in incognito windows as well, make sure to
 specify "spanning" mode for the <a href="manifest.html#incognito">incognito</a>
 manifest property.
 </p>
 
+<p class="note">
+<b>Note:</b>
+You cannot override the New Tab page in incognito windows.
+</p>
+
 <p>
 The following screenshots show the default New Tab page
 next to a custom New Tab page.
 </p>
 
 <table id="pics">
   <tr>
     <td> <b>The default New Tab page</b> </td>
     <td> <b>An alternative New Tab page</b> </td>
   </tr>
@@ skipping 92 matching lines @@
 <p>
 You can find simple examples of defining override pages in the
 <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/override/">examples/api/override</a>
 directory.
 For other examples and for help in viewing the source code, see
 <a href="samples.html">Samples</a>.
 </p>
 
 
 <!-- [PENDING: Maybe have a gallery of NTPs?] -->