Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -137,7 +137,7 @@ Plot.plot({
 })
 ```
 
-Plot now supports mark-level faceting via the new *mark*.**fx** and *mark*.**fy** options. Mark-level faceting makes it easier to control which marks are faceted (versus repeated across facets), especially when combining multiple datasets or specifying faceted annotations.
+Plot now supports [mark-level faceting](./README.md#facet-options) via the new *mark*.**fx** and *mark*.**fy** options. Mark-level faceting makes it easier to control which marks are faceted (versus repeated across facets), especially when combining multiple datasets or specifying faceted annotations.
 
 [<img src="./img/anscombe.png" width="640" alt="A faceted scatterplot of Anscombe’s quartet">](https://observablehq.com/@observablehq/plot-facets)