add legends guidance link

Author: gisellerosetta

vignettes/cookbook/_chart-types.Rmd

@@ -56,7 +56,7 @@ gapminder |>
 
 This line chart uses the afcharts theme and there are thin pale grey lines extending from the y axis. There are two thicker lines showing the life expectancy in the UK and China over time. The line colours are from the main Analysis Function palette - dark blue for China and orange for the UK, denoted by a legend at the bottom of the chart.
 
-An example with line labels and no legend can be found in the [annotations](#annotations) section.
+Legends should be avoided unless absolutely necessary, as these usually rely on using colour to match labels to data. More information can be found in the Analysis Function [charts guidance](https://analysisfunction.civilservice.gov.uk/policy-store/data-visualisation-charts/#section-11). It is best practice to label lines directly, and an example of this can be found in the [annotations](#Annotations) section.
 
 ## Bar charts