added some documentation

src/main/dig/processor/Processor.dig

@@ -242,7 +242,7 @@
         </entry>
         <entry>
           <string>Frequency</string>
-          <int>20</int>
+          <int>50</int>
         </entry>
       </elementAttributes>
       <pos x="1060" y="460"/>

src/main/java/de/neemann/digital/draw/model/RealTimeClock.java

@@ -43,7 +43,7 @@ public class RealTimeClock implements ModelStateObserver {
     public void handleEvent(ModelEvent event) {
         switch (event.getType()) {
             case STARTED:
-                if (frequency > 50)
+                if (frequency > 50)  // if frequency is high it is not necessary to update the GUI at every clock
                     output.removeObserver(GuiModelObserver.class);
 
                 int delay = 500 / frequency;