add full IANA time zone support

app/views/docs/index.html.erb

@@ -39,6 +39,9 @@
     <br><br>
 <pre>GET <span class="str"><%= @ssl_api_domain %>channels/9/fields/1/last.json?timezone=<span class="customcode">America%2FNew_York</span></span></pre>
     <br>
+    The most common time zone identifiers are listed below.  ThingSpeak supports all <a href="http://www.iana.org/time-zones" target="_blank">IANA Time Zone Database</a>
+    identifers; a <a href="http://twiki.org/cgi-bin/xtra/tzdatepick.html" target="_blank">human-readable list</a> is also available.
+    <br><br>
     <table class="table table-striped table-bordered table-condensed">
       <tr>
         <th>Identifier</th>