Add PNaCl release note about how to try out Subzero / which flag to set.

native_client_sdk/doc_generated/sdk/release-notes.html

Index: native_client_sdk/doc_generated/sdk/release-notes.html
diff --git a/native_client_sdk/doc_generated/sdk/release-notes.html b/native_client_sdk/doc_generated/sdk/release-notes.html
index 58762a832ad4fea2896572aea7e3d101e70331d1..a96ec9f12ccfb18f6a01304dae8163c6f1f99d3b 100644
--- a/native_client_sdk/doc_generated/sdk/release-notes.html
+++ b/native_client_sdk/doc_generated/sdk/release-notes.html
@@ -25,6 +25,16 @@ browser (version <code>Y</code>).</li>
 deprecated and will be removed in the next release. PNaCl has used libc++
 (which is much more up-to-date, currently based on LLVM 3.6) as the default
 since Pepper 33.</li>
+<li>PNaCl&#8217;s experimental <a class="reference external" href="https://chromium.googlesource.com/native_client/pnacl-subzero/+/master/README.rst">Subzero translator</a> is available for x86-32 NaCl in
+Chrome version 43, behind a flag. To give it a try, run Chrome with the
+<code>--enable-pnacl-subzero</code> commandline flag, and use the <code>optlevel 0</code>
+<a class="reference internal" href="/native-client/reference/nacl-manifest-format.html#pnacl-nmf-optlevels"><em>NaCl manifest option</em></a>. Application startup time
+should be several times faster than the previous LLVM-based <code>optlevel 0</code>
+mode, with similar code quality. Note that x86-32 NaCl requires a 32-bit
+Chrome. On Windows, it also requires a 32-bit Windows OS, but 64-bit Linux
+OSes can run x86-32 NaCl. If you try it out, please send us feedback
+on <a class="reference external" href="https://groups.google.com/forum/#!forum/native-client-dev">native-client-dev</a>. We are working on improvements and adding
+new targets.</li>
 </ul>
 <h3 id="pepper">Pepper</h3>
 <ul class="small-gap">