PB-1969 JS API: Add link to OL example #patch

As suggested by @pakb, it might be useful to add a link to a good OpenLayers example in the warning box of page "Javascript API".

Author: asteiner-swisstopo

docs/javascript-api.md

@@ -8,7 +8,7 @@ For more details, see [the GeoAdmin JS API specs](https://geoadmin.github.io/ol3
 
 The GeoAdmin JS API is about to be decommissioned and is not updated anymore.
 The default version is based on OpenLayers 3.6.0 from 2015.
-We strongly recommend using a different web mapping framework implementing the OGC WMTS, like Leaflet or plain OpenLayers.
+We strongly recommend using a different web mapping framework implementing the OGC WMTS, like Leaflet or plain OpenLayers as in [these examples for the XYZ service](/docs/xyz#openlayers).
 :::
 
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