add instruction about python-psutil

web/templates/servers.html

@@ -21,7 +21,7 @@
 	{% end %}
 
 	<p>
-		Run the <a href="/client/sysvitals_client">client</a> on a machine with the <code>--configure</code> flag to set up a new server. Your group ID and API key can be found on the <a href="/groups">groups page</a>.
+		Run the <a href="/client/sysvitals_client">client</a> on a machine with the <code>--configure</code> flag to set up a new server (you will need to install <code>python-psutil</code> or your distro's equivalent). Your group ID and API key can be found on the <a href="/groups">groups page</a>.
 		<br>
 		Run the client without arguments as a cronjob every minute:
 		<br>