Add repeat recipe of how to go from a matrix/grid on paper to repeats

For example, if you had this form on paper...

Use a repeat of kilns with a fixed repeat_count of 10. Then in each repeat, ask for each grade in a field-list with all required questions. Then at the bottom of that field list, add a note with a calculate that shows the sum and a constraint if that sum is not 100.

Start by locating the Sphinx documentation covering repeats, repeat_count, field-lists, notes, calculates, and constraints. Use the paper grid example from the issue as the basis for a recipe, and consider the work done when readers can follow it to build repeated grade entries whose total must equal 100.

Written by the indexing model from the issue text.