I would like to add custom labels to a `contour`

plot, replacing the `levels`

. Is this possible? MWE:

```
using Plots; pyplot() # other backend OK if necessary
using StatsBase
using Distributions
using StatsFuns
N = 100000
z = rand(MvNormal([1.0, 0.0], [1.0 0.5; 0.5 0.5]), N);
x = logistic.(z[1, :]);
y = logistic.(z[2, :]);
h = fit(Histogram, (x, y), closed = :left, nbins = (50, 50));
gap = trunc(Int, maximum(h.weights) / 9)
levels = 0:gap:(10*gap)
level_labels = map(x -> "$(x*10)%", 0:10)
contourf(midpoints(h.edges[1]),
midpoints(h.edges[2]),
h.weights';
levels = levels) # how to put level_labels in?
```