Add link to radiosonde serial number guide

Author: Mark Jessop

index.html

@@ -326,7 +326,7 @@ <h2><i class="icon-car rfloat"></i>Chase Mode</h2>
             <h3>Report Recovery</h3>
             <hr>
             <div class="row">
-            <span>You can report a recovery here. Enter the serial number (e.g. 'S1234567'), tick recovered/not recovered, and add some notes. If the sonde is not on the map, type its callsign into the top-left search box and press enter to retrieve historical data. You can then mark it as recovered. Optionally, you can use your location instead of the sonde's last location.</span>
+            <span>You can report a recovery here. Enter the serial number (e.g. 'S1234567'), tick recovered/not recovered, and add some notes. <a href="https://github.com/projecthorus/sondehub-infra/wiki/Radiosonde-Serial-Numbers" target="_blank" rel="noopener">Click here</a> for information on how to locate a sonde's serial number.</a> If the sonde is not on the map, type its serial into the top-left search box and press enter to retrieve historical data. You can then mark it as recovered. Optionally, you can use your location instead of the sonde's last location.</span>
             </div>
             <div class="row">
                 <span><b>Serial</b></span>