Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 *Not yet released. These are forthcoming changes in the main branch.*
 
-The new [density mark](./README.md#density) creates contours representing the [estimated density](https://en.wikipedia.org/wiki/Multivariate_kernel_density_estimation) of point clouds.
+The new [density mark](./README.md#density) creates contours representing the [estimated density](https://en.wikipedia.org/wiki/Multivariate_kernel_density_estimation) of two-dimensional point clouds. The **bandwidth** and number of **thresholds** can be configured.
 
 [<img src="./img/density-contours.png" width="640" height="400" alt="A scatterplot showing the relationship between the idle duration and eruption duration for Old Faithful">](https://observablehq.com/@observablehq/plot-density)
 
@@ -19,6 +19,20 @@ Plot.plot({
 })
 ```
 
+By default, the density is represented by contour lines. By setting the **fill** option to *density*, you can draw filled regions with a sequential color encoding instead.
+
+[<img src="./img/density-fill.png" width="640" height="500" alt="A contour plot showing the relationship between diamond price and weight">](https://observablehq.com/@observablehq/plot-density)
+
+```js
+Plot.density(diamonds, {x: "carat", y: "price", fill: "density"}).plot({
+  height: 500,
+  grid: true,
+  x: {type: "log"},
+  y: {type: "log"},
+  color: {scheme: "ylgnbu"}
+})
+```
+
 The new [linear regression marks](./README.md#linear-regression) produce [linear regressions](https://en.wikipedia.org/wiki/Linear_regression) with [confidence interval](https://en.wikipedia.org/wiki/Confidence_interval) bands, representing the estimated relation of a dependent variable (typically *y*) on an independent variable (typically *x*).
 
 [<img src="./img/linear-regression.png" width="640" height="400" alt="a scatterplot of penguin culmens, showing the length and depth of several species, with linear regression models by species and for the whole population, illustrating Simpson’s paradox">](https://observablehq.com/@observablehq/plot-linear-regression)