Add a usage example of the JLH score (#28905)

Adds a usage example of the JLH score used in significant terms aggregation.
All other methods to calculate significance score have such an example

Closes #28513

docs/reference/aggregations/bucket/significantterms-aggregation.asciidoc

@@ -327,6 +327,15 @@ However, the `size` and `shard size` settings covered in the next section provid
 ==== Parameters
 
 ===== JLH score
+The JLH score can be used as a significance score by adding the parameter
+
+[source,js]
+--------------------------------------------------
+
+	 "jlh": {
+	 }
+--------------------------------------------------
+// NOTCONSOLE
 
 The scores are derived from the doc frequencies in _foreground_ and _background_ sets. The _absolute_ change in popularity (foregroundPercent - backgroundPercent) would favor common terms whereas the _relative_ change in popularity (foregroundPercent/ backgroundPercent) would favor rare terms. Rare vs common is essentially a precision vs recall balance and so the absolute and relative changes are multiplied to provide a sweet spot between precision and recall.