calculate_tail_ratio: Calculate tail ratio
In cyplessen/tailRatio: What the Package Does (One Line, Title Case)

This function calculates tail ratios for two overlapping normal distributed populations.

1	calculate_tail_ratio(area, mean_high, sd_high, mean_low, sd_low, cutoff)

`area`	Area below or above a cutoff
`mean_high`	Mean of group with higher mean
`sd_high`	Standard deviation of group with higher mean
`mean_low`	Mean of group with lower mean
`sd_low`	Standard deviation of group with lower mean
`cutoff`	Cutoff value of interest, indicated in standard deviations from the higher mean group