sesman: comment on non-suid Xorg in sesman.ini

Pointed out by: #923

sesman/sesman.ini

@@ -71,7 +71,17 @@ param=-dpi
 param=96
 
 [Xorg]
+; Specify the path of non-suid Xorg executable. It might differ depending
+; on your distribution and version. The typical path is shown as follows:
+;
+; Fedora 26 or later    :  param=/usr/libexec/Xorg
+; Debian 9 or later     :  param=/usr/lib/xorg/Xorg
+; Ubuntu 16.04 or later :  param=/usr/lib/xorg/Xorg
+; Arch Linux            :  param=/usr/bin/Xorg or param=Xorg
+; CentOS 7              :  param=/usr/bin/Xorg or param=Xorg
+;
 param=Xorg
+; Leave the rest paramaters as-is unless you understand what will happen.
 param=-config
 param=xrdp/xorg.conf
 param=-noreset