Hook up the Buienradar provider metric in the forecast

Also, sync up the Luchtmeetnet provider documentation a bit.

src/main.rs

@@ -21,6 +21,7 @@ use rocket::tokio::{self, select};
 use rocket::{get, routes, FromFormField, State};
 
 use self::maps::{Maps, MapsHandle};
+use self::providers::buienradar::Item as BuienradarItem;
 use self::providers::luchtmeetnet::Item as LuchtmeetnetItem;
 
 pub(crate) mod maps;
@@ -69,7 +70,7 @@ struct Forecast {
 
     /// The precipitation (when asked for).
     #[serde(skip_serializing_if = "Option::is_none")]
-    precipitation: Option<()>,
+    precipitation: Option<Vec<BuienradarItem>>,
 
     /// The UV index (when asked for).
     #[serde(rename = "UVI", skip_serializing_if = "Option::is_none")]
@@ -154,7 +155,9 @@ async fn forecast(
             Metric::PAQI => forecast.paqi = Some(()),
             Metric::PM10 => forecast.pm10 = providers::luchtmeetnet::get(lat, lon, metric).await,
             Metric::Pollen => forecast.pollen = Some(()),
-            Metric::Precipitation => forecast.precipitation = Some(()),
+            Metric::Precipitation => {
+                forecast.precipitation = providers::buienradar::get(lat, lon, metric).await
+            }
             Metric::UVI => forecast.uvi = Some(()),
         }
     }

src/providers/luchtmeetnet.rs

@@ -25,12 +25,13 @@ struct Container {
 #[derive(Debug, Deserialize, Serialize)]
 #[serde(crate = "rocket::serde")]
 pub(crate) struct Item {
-    /// The time for when the value is forecast.
+    /// The time(stamp) of the forecast.
     #[serde(
         rename(deserialize = "timestamp_measured"),
         serialize_with = "ts_seconds::serialize"
     )]
     time: DateTime<Utc>,
+
     /// The forecasted value.
     ///
     /// The unit depends on the selected [metric](Metric).
@@ -39,6 +40,12 @@ pub(crate) struct Item {
 
 /// Retrieves the Luchtmeetnet forecasted items for the provided position and metric.
 ///
+/// It supports the following metrics:
+/// * [`Metric::AQI`]
+/// * [`Metric::NO2`]
+/// * [`Metric::O3`]
+/// * [`Metric::PM10`]
+///
 /// Returns [`None`] if retrieval or deserialization fails, or if the metric is not supported by
 /// this provider.
 pub(crate) async fn get(lat: f64, lon: f64, metric: Metric) -> Option<Vec<Item>> {