add 2+ example in man page

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ION2C <- function(b, y){
    Hydrogen <- 1.007825
    Oxygen <- 15.994915
    Nitrogen <- 14.003074

    #yo <- fi$y - Oxygen - Hydrogen - Hydrogen
    c <- b + (Nitrogen + (3 * Hydrogen))
    z <- y - (Nitrogen + (3 * Hydrogen))

    b2 <- (b + Hydrogen) / 2
    y2 <- (y + Hydrogen) / 2

    return(cbind(b, y, b2 ,y2))
}

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DONE