Add undetected hdmi resolution to X11/Xorg

Mini tutorial

I am putting here some notes for posterity

In the current version of armbian (testing H6) I use X11 / Xorg only reaches 1024x768, but my display reaches 1440x900.
To add this new resolution to the list of Settings/Display you have to give these commands:

# xrandr --listmonitors

(this command serves to see what it's called, the hdmi output)

# cvt 1440 900

(output: 
# 1440x900 59.89 Hz (CVT 1.30MA) hsync: 55.93 kHz; pclk: 106.50 MHz
Modeline "1440x900_60.00"  106.50  1440 1528 1672 1904  900 903 909 934 -hsync +vsync )

# xrandr --newmode "1440x900_60.00" 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync

# xrandr --addmode HDMI-1 1440x900_60.00

# xrandr --output HDMI-1 --mode 1440x900_60.00

If it works then modify Xorg with:

# sudo mcedit /etc/X11/xorg.conf.d/40-monitor.conf

Section "Monitor"
Identifier "HDMI-1"
Modeline "1440x900_60.00" 106.50 1440 1528 1672 1904 900 903 909 934 -hsync +vsync
Option "PreferredMode" "1440x900"
EndSection

# reboot