[DOCS] Add supported OSs and platforms to the SDK download page.

native_client_sdk/doc_generated/sdk/download.html

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 <section id="download-the-native-client-sdk">
 <span id="download"></span><h1 id="download-the-native-client-sdk"><span id="download"></span>Download the Native Client SDK</h1>
 <p>This page provides an overview of the Native Client SDK, and instructions for
 downloading and installing the SDK.</p>
 <div id="home">
 <a class="button-nacl button-download" href="http://storage.googleapis.com/nativeclient-mirror/nacl/nacl_sdk/nacl_sdk.zip">Download SDK Zip File</a>
 </div><h2 id="overview"><span id="sdk-overview"></span>Overview</h2>
 <p>The Native Client SDK includes:</p>
@@ skipping 29 matching lines @@
 <ul class="small-gap">
 <li>On the Mac, you need to install <code>make</code> on your system before you can build
 and run the examples in the SDK. One easy way to get <code>make</code>, along with
 several other useful tools, is to install <a class="reference external" href="https://developer.apple.com/technologies/tools/">Xcode Developer Tools</a>. After installing Xcode,
 go to the XCode menu, open the Preferences dialog box then select Downloads
 and Components. Verify that Command Line Tools are installed. If you&#8217;d rather
 not install Xcode, you can download and build an <a class="reference external" href="http://mac.softpedia.com/dyn-postdownload.php?p=44632&amp;t=4&amp;i=1">open source version</a> of <code>make</code>.
 To build the program you may also need to download and install <a class="reference external" href="https://github.com/kennethreitz/osx-gcc-installer">gcc</a>.</li>
 <li>On Windows, the Native Client SDK includes a copy of GNU Make.</li>
 </ul>
-<h2 id="versioning"><span id="id3"></span>Versioning</h2>
+<h2 id="platforms"><span id="id3"></span>Platforms</h2>
+<p>Native Client supports several operating systems, including Windows, Linux, OSX,
+and ChromeOS. It supports several architectures including on x86-32, x86-64,
+ARM, and MIPS.</p>
+<h2 id="versions"><span id="versioning"></span>Versions</h2>
 <p>Chrome is released on a six week cycle, and developer versions of Chrome are
 pushed to the public beta channel three weeks before each release. As with any
 software, each release of Chrome may include changes to Native Client and the
 Pepper interfaces that may require modification to existing applications.
 However, modules compiled for one version of Pepper/Chrome should work with
 subsequent versions of Pepper/Chrome. The SDK includes multiple versions of the
 Pepper APIs to help developers make adjustments to API changes and take
 advantage of new features: <a class="reference external" href="/native-client/pepper_stable">stable</a>, <a class="reference external" href="/native-client/pepper_beta">beta</a> and <a class="reference external" href="/native-client/pepper_dev">dev</a>.</p>
 <h2 id="installing-the-sdk"><span id="id4"></span>Installing the SDK</h2>
 <h3 id="downloading-and-unzipping"><span id="id5"></span>Downloading and Unzipping</h3>
@@ skipping 156 matching lines @@
 information about the SDK and new bundles.</li>
 <li>If you&#8217;re just starting with Native Client, we recommend reading the
 <a class="reference external" href="../overview">Technical Overview</a> and walking through the
 <a class="reference external" href="devguide/tutorial/tutorial-part1">Getting Started Tutorial</a>.</li>
 <li>If you&#8217;d rather dive in, see
 <a class="reference external" href="devguide/devcycle/building">Building Native Client Modules</a>.</li>
 </ul>
 </section>
 
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