docs: add preview sdk docs to provide an api overview and install steps,
enable the 'preview' flag for the docs build
revise sdk side nav for preview

Change-Id: Ifc26cfb1f18e394e96853fd42f0e194d5f8552f3
diff --git a/docs/html/sdk/index.jd b/docs/html/sdk/index.jd
index 8b77303..4153951 100644
--- a/docs/html/sdk/index.jd
+++ b/docs/html/sdk/index.jd
@@ -19,6 +19,7 @@
 
 @jd:body
 
+<div class="non-preview">
 <p>Here's an overview of the steps you must follow to set up the Android SDK:</p>
 
 <ol>
@@ -32,3 +33,4 @@
 
 <p>To get started, download the appropriate package from the table above, then read the guide to <a
 href="installing.html">Installing the SDK</a>.</p>
+</div>