Setting MAC address extra possibility

[PanderMusubi]

After this line https://github.com/armbian/documentation/blame/master/docs/User-Guide_Basic-Troubleshooting.md#L98 some text should be added similar to:

If there is no file `Wired connection 1.nmconnection`, one can try to edit the that connection by running `nmtui`. However, it is possible that this also doesn't work if the MAC address is generated randomly.

See also the answer to issue #321 to improve the phrasing.

[PanderMusubi]

Perhaps also mention in the part on /etc/network/interfaces that if the line

# Network is managed by Network manager

that it is bettor to follow the steps related to Network manager below.