(docs) Add additional information to FAQ about split keyboards

[mcrosson]

Added additional information on how to pair splits as well as TRRS wires providing power when using batteries to the FAQ

[tominabox1]

The zmk terminology is "central" and "peripheral" when referring to the "primary" and "non-primary" halves. I think you want to use those terms here. It might also be worthwhile to note that split primaries will show up as $keyboard Left by default.

[mcrosson]

The zmk terminology is "central" and "peripheral" when referring to the "primary" and "non-primary" halves. I think you want to use those terms here. It might also be worthwhile to note that split primaries will show up as $keyboard Left by default.

Nice catch. Updated the PR accordingly.

[tominabox1]

Cool! lgtm!