Add description for Stookwijzer get_forecast service (#37476)

Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_integrations/stookwijzer.markdown

@@ -30,3 +30,82 @@ Additionally, various sensor entities are provided:
 - **Air Quality Index**: Sensor containing the air quality index at the selected location.
 
 {% include integrations/config_flow.md %}
+
+## Action: Get Forecast
+
+The `stookwijzer.get_forecast` action populates [response data](/docs/scripts/perform-actions#use-templates-to-handle-response-data)
+with a mapping of the Stookwijzer advice forecast.
+
+```yaml
+action: stookwijzer.get_forecast
+target:
+  config_entry_id: 12345
+response_variable: stookwijzer_forecast
+```
+
+The response data field contains the `forecast` field.
+`forecast` is a list of forecast advice entries at a given time:
+
+| Response data | Description                                                                 | Example                   |
+|--------------|-----------------------------------------------------------------------------|---------------------------|
+| `datetime`   | The time of the forecasted advice.                                         | 2025-01-14T14:00:00+00:00 |
+| `advice`     | The forecasted advice code.                                               | code_yellow               |
+| `final`      | Indicator whether the advice is final or can still change.                | True                      |
+
+{% details "Example action response" %}
+
+```yaml
+forecast:
+  - datetime: "2025-02-12T17:00:00+01:00"
+    advice: code_yellow
+    final: True
+  - datetime: "2025-02-12T23:00:00+01:00"
+    advice: code_yellow
+    final: True
+  - datetime: "2025-02-13T05:00:00+01:00"
+    advice: code_orange
+    final: False
+  - datetime: "2025-02-13T11:00:00+01:00"
+    advice: code_red
+    final: False
+```
+
+{% enddetails %}
+
+## Examples
+
+{% details "Example template sensor using get_forecast" %}
+
+Example template sensors containing the Stookwijzer forecast for 6 and 12 hours from now.
+
+{% raw %}
+
+```yaml
+template:
+  - trigger:
+      - trigger: time_pattern
+        hours: /1
+    action:
+      - action: stookwijzer.get_forecast
+        target:
+          entity_id: sensor.stookwijzer_advice_code
+        response_variable: advice_forecast
+    sensor:
+      - name: Stookwijzer forecast 6 hours
+        unique_id: stookwijzer_forecast_6_hours
+        state: "{{ advice_forecast['forecast'][0]['advice'] }}"
+        attributes:
+          final: "{{ advice_forecast['forecast'][0]['final'] }}"
+          timestamp: "{{ advice_forecast['forecast'][0]['datetime'] }}"
+      - name: Stookwijzer forecast 12 hours
+        unique_id: stookwijzer_forecast_12_hours
+        state: "{{ advice_forecast['forecast'][1]['advice'] }}"
+        attributes:
+          final: "{{ advice_forecast['forecast'][1]['final'] }}"
+          timestamp: "{{ advice_forecast['forecast'][1]['datetime'] }}"
+```
+
+{% endraw %}
+
+{% enddetails %}
+