mention OL file location

Author: jmckenna

en/cgi/openlayers.txt

@@ -100,3 +100,15 @@ Customizing settings
 * environment variables::
 
     MS_OPENLAYERS_JS_URL - The URL to the OpenLayers javascript library. Per default the library loaded from the MapServer web server.
+
+Location of the embedded OpenLayers.js file
+-------------------------------------------
+
+If you aren't providing your own OpenLayers library through `MS_OPENLAYERS_JS_UR`, 
+MapServer will point to a hardcoded filepath of `www.mapserver.org/lib` to find the OpenLayers 
+library, referred to in [maptemplate.c](https://github.com/MapServer/MapServer/blob/main/src/maptemplate.c#L54).
+
+The contents on that `lib` folder is stored in the MapServer documentation repository, 
+in the [/extra](https://github.com/MapServer/MapServer-documentation/tree/main/extra) folder.
+You are warmly encouraged to contribute to upgrading the OpenLayers library, at any time (maybe start 
+with creating a new [Pull Request](https://github.com/MapServer/MapServer-documentation/pulls) there.