Update README

Author: mbostock

README.md

@@ -745,7 +745,7 @@ Returns a new arrow with the given *data* and *options*.
 
 [<img src="./img/bar.png" width="320" height="198" alt="a bar chart">](https://observablehq.com/@observablehq/plot-bar)
 
-[Source](./src/marks/bar.js) · [Examples](https://observablehq.com/@observablehq/plot-bar) · Draws rectangles where *x* is ordinal and *y* is quantitative ([Plot.barY](#plotbarydata-options)) or *y* is ordinal and *x* is quantitative ([Plot.barX](#plotbarxdata-options)). There is usually one ordinal value associated with each bar, such as a name, and two quantitative values defining a lower and upper bound. The lower bound is often not specified explicitly because it defaults to zero as in a conventional bar chart.
+[Source](./src/marks/bar.js) · [Examples](https://observablehq.com/@observablehq/plot-bar) · Draws rectangles where *x* is ordinal and *y* is quantitative ([Plot.barY](#plotbarydata-options)) or *y* is ordinal and *x* is quantitative ([Plot.barX](#plotbarxdata-options)). If one dimension is temporal and the other is quantitative, as in a time-series bar chart, use the [rect mark](#rect) with the *interval* option instead. There is usually one ordinal value associated with each bar, such as a name, and two quantitative values defining a lower and upper bound. The lower bound is often not specified explicitly because it defaults to zero as in a conventional bar chart.
 
 For the required channels, see [Plot.barX](#plotbarxdata-options) and [Plot.barY](#plotbarydata-options). The bar mark supports the [standard mark options](#marks), including insets and rounded corners. The **stroke** defaults to none. The **fill** defaults to currentColor if the stroke is none, and to none otherwise.