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

native_client_sdk/doc_generated/sdk/download.html

Index: native_client_sdk/doc_generated/sdk/download.html
diff --git a/native_client_sdk/doc_generated/sdk/download.html b/native_client_sdk/doc_generated/sdk/download.html
index 9045bb9c188886cee233accdfa3cbb805c3da8ef..ea60d8e8fbf24d85f47526cd39752a7961eda212 100644
--- a/native_client_sdk/doc_generated/sdk/download.html
+++ b/native_client_sdk/doc_generated/sdk/download.html
@@ -47,7 +47,11 @@ not install Xcode, you can download and build an <a class="reference external" h
 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