[User Manual] Added example when less than 16cells are used.

[jalinei]

• Added a different color for BMS power signals (first and last wires of the harness)
• Added a connection example for a 12s battery so that it is easier to understand how to wire the harness.
• Added a zoom view to explain what "exposed pads" refers to.

[github-actions[bot]]

Diff between main (7b6ec8e) and main (873115e):

• bms-c1-diff_sch.pdf
• bms-c1-diff_pcb.pdf

[jalinei]

[09bfa76] I've added this minor change to the PR. It simplifies the user experience when looking how to flash the newest firmware.