Use non-adjacent position in the toy example

[hyanwong]

I think it's a bit confusing that the toy example in the docs uses positions 0, 1, 2, 3, 4, 5. You therefore can't tell if the "Site:" label is referring to the site id or the site position.

If the site position, then values of 0 might seem very weird to bioinformatics people, who are used to counting positions from 1. Perhaps we can get around that by starting e.g. at position (say) 4?