Improve Chrome OS VPN API documentation

chrome/common/extensions/docs/templates/intros/vpnProvider.html

 <h2 id="usage">Usage</h2>
 <p>
 Typical usage of vpnProvider is as follows:
 
 <ul>
   <li>Create VPN configurations using the $(ref:createConfig) method. A VPN
     configuration is a persistent entry shown to the user in a native Chrome OS
     UI. The user can select a VPN configuration from a list and connect to it or
     disconnect from it.</li>
   <li>Add listeners to the events $(ref:onPlatformMessage),
     $(ref:onPacketReceived) and $(ref:onConfigRemoved).</li>
   <li>When the user connects to the VPN configuration, $(ref:onPlatformMessage)
     will be received with the message <code>"connected"</code>. We refer to the
     period between the messages <code>"connected"</code> and
     <code>"disconnected"</code> as a VPN session. In this time period, the
     extension that receives the message is said to own the VPN session.</li>
   <li>Initiate connection to the VPN server and start the VPN client.</li>
   <li>Set the Parameters of the connection using $(ref:setParameters).</li>
   <li>Notify the connection state as <code>"connected"</code> using
     $(ref:notifyConnectionStateChanged).</li>
   <li>When the steps above are completed without errors, a virtual tunnel is
     created to the network stack of Chrome OS. IP packets can be sent through
-    the tunnel using $(ref:sendPacket) and any incoming packets will be received
-    using the event $(ref:onPacketReceived).</li>
+    the tunnel using $(ref:sendPacket) and any packets originating on the Chrome
+    OS device will be received using the event $(ref:onPacketReceived).</li>
   <li>When the user disconnects from the VPN configuration,
     $(ref:onPlatformMessage) will be fired with the message
     <code>"disconnected"</code>.</li>
   <li>If the VPN configuration is no longer necessary, it can be destroyed using
     $(ref:destroyConfig).</li>
 </ul>
 </p>