add a link to plot/features/scales#interval (#1531)

Author: Fil

docs/features/scales.md

@@ -604,7 +604,7 @@ Plot.plot({
 [Mark transforms](./transforms.md) typically consume values *before* they are passed through scales (_e.g._, when binning). In this case the mark transforms will see the values prior to the scale transform as input, and the scale transform will apply to the *output* of the mark transform.
 :::
 
-The **interval** scale option sets an ordinal scale’s **domain** to the start of every interval within the extent of the data. In addition, it implicitly sets the **transform** of the scale to *interval*.floor, rounding values down to the start of each interval. For example, below we generate a time-series bar chart; when an **interval** is specified, missing days are visible.
+The **interval** scale option<a id="interval" class="header-anchor" href="#interval" aria-label="Permalink to &quot;interval&quot;"></a> sets an ordinal scale’s **domain** to the start of every interval within the extent of the data. In addition, it implicitly sets the **transform** of the scale to *interval*.floor, rounding values down to the start of each interval. For example, below we generate a time-series bar chart; when an **interval** is specified, missing days are visible.
 
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