updated IGH installation procedure

[ros2torial]

previous commands were creating some errors like -

• "cp: cannot create regular file '/etc/sysconfig/ethercat': No such file or directory"
• "bash: /etc/udev/rules.d/99-EtherCAT.rules: Permission denied"

New changes resolve the issue and can be directly converted into a single shell file to run without error.

[mcbed]

thanks !