added prometheseus.histogramQuantile function

content/v2.0/reference/flux/stdlib/experimental/prometheus/histogramquantile.md

@@ -0,0 +1,46 @@
+---
+title: prometheus.histogramQuantile() function
+description: >
+  The `prometheus.histogramQuantile()` function calculates quantiles on a set of values
+  assuming the given histogram data is scraped or read from a Prometheus data source.
+menu:
+  v2_0_ref:
+    name: prometheus.histogramQuantile
+    parent: Prometheus
+weight: 301
+---
+
+The `prometheus.histogramQuantile()` function calculates quantiles on a set of values
+assuming the given histogram data is scraped or read from a Prometheus data source.
+
+_**Function type:** Aggregate_
+
+{{% warn %}}
+The `prometheus.histogramQuantile()` function is currently experimental and subject to change at any time.
+By using this function, you accept the [risks of experimental functions](/v2.0/reference/flux/stdlib/experimental/#use-experimental-functions-at-your-own-risk).
+{{% /warn %}}
+
+```js
+import "experimental/prometheus"
+
+prometheus.histogramQuantile(
+  quantile: 0.99
+)
+```
+
+## Parameters
+
+### quantile
+A value between 0.0 and 1.0 indicating the desired quantile.
+
+_**Data type:** Float_
+
+## Examples
+
+### Calculate the 99th quantile in Prometheus data
+```js
+import "experimental/prometheus"
+
+prometheus.scrape(url: "https://example-url.com/metrics")
+  |> prometheus.histogramQuantile(quantile: 0.99)
+```