Update usage instruction

[Et7f3]

old instruction seems no-op and no error message

robox/robox.sh

Line 120 in bce13e9

ROBOX_TAGS=`grep -E '"name":' $ROBOX_FILES | awk -F'"' '{print $4}' | grep "generic" | sed "s/generic-/roboxes\//g" | sed "s/\-\(hyperv\|vmware\|libvirt\|parallels\|virtualbox\|docker\)\-\(x32\|x64\|a32\|a64\|p32\|p64\|r32\|r64\|m32\|m64\)\$//g" | sort -V -u --field-separator=-`