It looks like xtable.hints is provided by the package but isn't properly exported so you can't actually use it. It's a fairly simple function though and the easiest solution would probably be to just copy the source and make your own function that does the exact same thing.
xtable.hints <- function(x, align = "llll", ...){
x <- as.data.frame(x$results[, c(2, 1, 3)])
colnames(x) <- c("Package", "Function", "Task")
xtable(x, align = align, ...)
}
x <- 1:10
y <- rnorm(10)
o <- lm(y~x)
xtable(hints(o)) # now it works