c-c++: Add notes on related layers.
c-c++: Add notes on related layers.

Signed-off-by: Magnus Therning <9f4ca770b638615ac5c3e0d2da16b77c80c2f2c6@therning.org>

tsonntag/dotemacs,tsonntag/dotemacs,tsonntag/dotemacs,tsonntag/dotemacs