reff incorrectly documented

[sethaxen]

reff is documented as the relative efficiency of the unsmoothed ratios:

PSIS.jl/src/core.jl

Lines 25 to 26 in 35b9e71

	- `reff`: the ratio of the effective sample size of the unsmoothed importance ratios and
	the actual sample size.

PSIS.jl/src/core.jl

Lines 189 to 192 in 35b9e71

	- `reff::Union{Real,AbstractArray}`: the ratio(s) of effective sample size of
	`log_ratios` and the actual sample size `reff = ess/(draws * chains)`, used to account
	for autocorrelation, e.g. due to Markov chain Monte Carlo. If an array, it must have the
	size `(parameters...,)` to match `log_ratios`.

However, reff should be the relative efficiency of the inverse of the unsmoothed ratios. See e.g. the docstring for loo::psis : https://github.com/stan-dev/loo/blob/b94b2b148e55ece22b83ef5995e0e4b98ff1abe0/R/psis.R#L16-L26