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).
I find "This modifies the condition option" misleading. To me this condition determines if "feature selection toggling" is on.