ice40: Adding carry-chain routing diagram.
ice40: Adding carry-chain routing diagram.

Editable version at
https://docs.google.com/drawings/d/1ZG3eqAp7NrDsf6Ra6zHrVOJyxxCmblpOPVFW8NpE4aQ/edit

Signed-off-by: Tim 'mithro' Ansell <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@mith.ro>

SymbiFlow/symbiflow-arch-defs,SymbiFlow/symbiflow-arch-defs