Update facet-plots.md

Author: nicolaskruchten

Diff for: doc/python/facet-plots.md

@@ -129,7 +129,7 @@ fig.show()
 
 *introduced in plotly 4.12*
 
-The `.add_trace()` method can be used to add a copy of the same trace to each facet, for example an overall linear regression line as below. The `legendgroup`/`showlegend` pattern below is recommended to avoid having a separate legend item for each copy of the trace.
+The `.add_trace()` method can be used to add a copy of the same trace to each facet, for example an overall linear regression line as below. The `legendgroup`/`showlegend` pattern below is recommended to avoid having a separate legend item for each copy of the trace. Note that as of v5.2.1, there is [a built-in option to add an overall trendline to all facets](https://plotly.com/python/linear-fits/) that uses this technique under the hood.
 
 ```python
 import plotly.express as px