Add instruction to put resistor/jumper on UART port

[izuannazrin]

I think it's better to mention the missing resistor at header J2. Had my head scratching wondering why there are no output until I stumbled on one of your post in the forum XD

~~Also I noticed the console mentioned in kernel cmdline is ttyAMA1, meanwhile output stop after mentioning ttyAMA0. Could it be there are another UART port on board?hmm~~ Wrong lead, sorry. ttyAMA1 is correct, as seen from other huawei devices' bootlog.