Add documentation for clipboardRead and clipboardWrite permissions.

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

 <div id="pageData-name" class="pageData">Formats: Manifest Files</div>
 <div id="pageData-showTOC" class="pageData">true</div>
 
 <p>
 Every extension, installable web app, and theme has a
 <a href="http://www.json.org">JSON</a>-formatted manifest file,
 named <code>manifest.json</code>,
 that provides important information.
 </p>
 
@@ skipping 349 matching lines @@
   <td> Required if the extension uses the
        "chrome://favicon/<em>url</em>" mechanism
        to display the favicon of a page.
        For example, to display the favicon of http://www.google.com/,
        you declare the "chrome://favicon/" permission
        and use HTML code like this:
        <pre>&lt;img src="chrome://favicon/http://www.google.com/"></pre>
        </td>
 </tr>
 <tr>
+  <td> "clipboardRead" </td>
+  <td> Required if the extension uses
+       <code>document.execCommand('paste')</code>. </td>
+</tr>
+<tr>
+  <td> "clipboardWrite" </td>
+  <td> Recommended if an extension uses
+       <code>document.execCommand('copy')</code> or
+       <code>document.execCommand('cut')</code>. Required for an app.</td>
+</tr>
+<tr>
   <td> "contextMenus" </td>
   <td> Required if the extension uses the
        <a href="contextMenus.html">chrome.contextMenus</a> module. </td>
 </tr>
 <tr>
   <td> "cookies" </td>
   <td> Required if the extension uses the
        <a href="cookies.html">chrome.cookies</a> module. </td>
 </tr>
 <tr>
@@ skipping 104 matching lines @@
 A missing integer is equal to zero.
 For example, 1.1.9.9999 is newer than 1.1.
 </p>
 
 <p>
 For more information, see
 <a href="autoupdate.html">Autoupdating</a>.
 </p>
 
 <!-- [PENDING: Possibly: point to the store/dashboard and make a big deal of the fact that autoupdating is free if you use them.] -->