Further improve MapFilter documentation

src/topics/MapFilter.md

@@ -1,5 +1,9 @@
 The [`MapFilter`](../references/qwc2_plugins.md#mapfilter) plugin allows filtering the map content via QGIS Server WMS FILTER.
 
+It can be configured to support predefined filters, geometry filters, temporal filters and custom filters, see [`MapFilter`](../references/qwc2_plugins.md#mapfilter).
+
+*Note*: Geometry filters requires the `filter_geom` plugin from [qwc-qgis-server-plugins](https://github.com/qwc-services/qwc-qgis-server-plugins), and the filter will currently only be applied to postgis layers.
+
 You can set predefined filter expressions for a theme item as follows:
 
 ```json