Improve docs for interaction.Select

Attempts to make the options clearer.

I find the current option names 'condition' and 'toggle' rather confusing. ISTM that 'condition' should be called 'toggle' (a simple select/unselect toggle), and 'toggle' should be called 'modifier' (or something similar).
though the same is also true of the add/remove options. I'll close this PR for the moment, and see I can come up with some better wording