A reppop table in 'gscramble' is used to define how the founder populations
in a GSP (typically named something like "A", "B", etc.) are mapped to the
groups/populations of individuals, as specified in the individual meta data
(an example of which is found in I_meta).
A tibble with three columns: index, which must be of type integer,
pop, and group of type character.
The developers created this.
This particular version shows a situation where individuals from group Pop1 will be
sampled as founders from A and from group Pop2 will be sampled as founders from
B into the GSP. Since this RepPop1 example has two values of index: 1 and 2,
it specifies that individuals from the populations will be sampled without replacment,
two times into the founders on the pedigree.