Mention telnet in debugging tips

[ClearStaff]

While trying to port droidian to Xiaomi Mi Pad 5 i encountered issue where i could not mount filesystem with initrd.
The only way in which i found out what is wrong was using telnet.

Please mention the usage of dmesg over telnet in porting guide to help newcomers.

[FakeShell]

hello, feel free to open a pr adding that to debugging tips -> pre boot tips