Add note to explain why vismodel may fail

[Bisaloo]

I think this issue will become more and more common. The current vismodel error is:

library(pavo)
#> Welcome to pavo 2! Take a look at the latest features (and update your bibliography) in our recent publication: Maia R., Gruson H., Endler J. A., White T. E. (2019) pavo 2: new tools for the spectral and spatial analysis of colour in R. Methods in Ecology and Evolution, 10, 1097-1107.
data(flowers)

flowers_NIR <- as.rspec(flowers, lim = c(300, 1200))
#> wavelengths found in column 1
#> Warning in as.rspec(flowers, lim = c(300, 1200)): Interpolating beyond the range
#> of actual data. Check 'lim' and `exceed.range` arguments to confirm this is the
#> desired behaviour.

vismodel(flowers_NIR)
#> Error in vismodel(flowers_NIR): wavelength range in spectra and visual system data do not match

^{Created on 2020-02-18 by the reprex package (v0.3.0)}

but it doesn't pinpoint the exact source of the issue and how to solve it. This might help?

[thomased]

Yep, agreed. Sensible.