MTB4 - Improve test procedure step descriptions

[MSECode]

Task

We need to improve the description of some steps of the test for the MTB4 boards in order to make it easier to complete. Specifically the improvements are:

• After 3.2 specify how to connect cable to the board and how to put it in the test setup
• specify to mount the board for fw flash

Definition of Done - DoD

• procedure is improved

cc: @valegagge