Vnc x11 updates

docs.it4i/general/accessing-the-clusters/graphical-user-interface/vnc.md

@@ -76,7 +76,7 @@ username :102
 ```
 
 !!! note
-    The VNC server runs on port 59xx, where xx is the display number. So, you get your port number simply as 5900 + display number, in our example 5900 + 61 = 5961. Another example for display number 102 is calculation of TCP port 5900 + 102 = 6002. **Please, calculate your own port number and use it instead of 5961 from examples below!**
+    The VNC server runs on port 59xx, where xx is the display number. So, you get your port number simply as 5900 + display number, in our example 5900 + 61 = 5961. Another example for display number 102 is calculation of TCP port 5900 + 102 = 6002 but be aware, that TCP ports above 6000 are often used by X11. **Please, calculate your own port number and use it instead of 5961 from examples below!**
 
 To access the VNC server you have to create a tunnel between the login node using TCP port 5961 and your machine using a free TCP port (for simplicity the very same) in next step. See examples for [Linux/Mac OS](#linuxmac-os-example-of-creating-a-tunnel) and [Windows](#windows-example-of-creating-a-tunnel).