Mention cpu usage

webadmin/EN/help_icecast.html

@@ -124,6 +124,8 @@
 
     <p class="helptext">This system isn't intended to broadcast to large audiences and the upper limit of listeners is set at ten. So a family and friends type group.</p>
 
+    <p class="helptext">Icecast is quite CPU intensive. For example on an A20 based system it takes about 70% of the CPU resource. This is something to be aware of if you're running multiple apps</p>
+
     <p class="subheadertext">Adding music</p>
 
     <p class="helptext"><b>1.</b> Add mp3 or ogg files to a USB drive</p>