Move discussion of congeneric series to multiple calculations paper

[fjclark]

Proposed Change

Move discussion of congeneric series (within "Simulation prerequisites") to multiple calculations paper and replace with a short paragraph explaining that we assume alignment is easy here.

This is a trivial change which I am happy to make unless there are any objections to restructuring like this.

Proposed Authors and Reviewers

Please volunteer (before the end of January) to author/ review and state when you're available. Authors, please say roughly when you plan to contribute the changes (no later than the end of May).

Proposed author: I'm happy to do this in January
Proposed reviewer: This almost doesn't need reviewing but maybe @ppxasjsm can confirm that this is sensible and briefly check?