[Rd] Clarify documentation of nlme::varIdent

[Roland Fuß]

Hello,

The documentation of nlme::varIdent says this:

"the coefficients of the variance function represent the ratios between 
the variances and a reference variance (corresponding to a reference 
group level)"

However, the parameter estimate shown in the summary output for lme 
models is the ratio between standard deviations. Could this be clarified 
in the documentation, e.g., by adding Eq. 5.13 from Pinheiro and Bates 
(2000)?

-- 
Dr. Roland Fuß

Thünen-Institut für Agrarklimaschutz/
Thünen Institute of Climate-Smart Agriculture