Add migration to WebAssembly information to PNaCl / NaCl docs.

native_client_sdk/doc_generated/reference/nacl-manifest-format.html

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-<section id="native-client-manifest-nmf-format">
+<b><font color="#cc0000">
+NOTE:
+Deprecation of the technologies described here has been announced
+for platforms other than ChromeOS.<br/>
+Please visit our
+<a href="/native-client/migration">migration guide</a>
+for details.
+</font></b>
+<hr/><section id="native-client-manifest-nmf-format">
 <h1 id="native-client-manifest-nmf-format">Native Client Manifest (nmf) Format</h1>
 <div class="contents local" id="contents" style="display: none">
 <ul class="small-gap">
 <li><a class="reference internal" href="#overview" id="id1">Overview</a></li>
 <li><a class="reference internal" href="#field-summary" id="id2">Field summary</a></li>
 <li><p class="first"><a class="reference internal" href="#field-details" id="id3">Field details</a></p>
 <ul class="small-gap">
 <li><a class="reference internal" href="#program" id="id4">program</a></li>
 <li><a class="reference internal" href="#files" id="id5">files</a></li>
 </ul>
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 representing the contents of the file. Specifying the <code>nmf</code> contents
 inline with a data URI can help reduce the amount of network traffic
 required to load the Native Client application.</p>
 <h3 id="url-resolution"><span id="nmf-url-resolution"></span>URL resolution</h3>
 <p>All URLs contained in a manifest are resolved relative to the URL of
 the manifest. If the manifest was specified as a data URI, the URLs must
 all be absolute.</p>
 </section>
 
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