diff --git a/README.md b/README.md
index c314148..588ecb4 100644
--- a/README.md
+++ b/README.md
@@ -192,3 +192,25 @@ maxHeight:
 
 Note: Elevation profiles are only supported if exactly one track is present.
 ```
+
+### Configuration options
+
+There are a number of module-specific options you can add to your site configuration under the `params.modules.leaflet` key.
+For example, in a YAML config file:
+
+```yaml
+params:
+  modules:
+    leaflet:
+      com_thunderforest_outdoors:
+        apiKey: YOUR_API_KEY_GOES_HERE
+      com_thunderforest_cycle:
+        apiKey: YOUR_API_KEY_GOES_HERE
+      com_thunderforest_landscape:
+        apiKey: YOUR_API_KEY_GOES_HERE
+```
+
+
+| Key                 | Description                                                                                                                                                                                                                                                                 |
+| ------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `<layer_id>.apiKey` | API key for the layer with the given ID. Note that the layer ID is the same as in the `leaflet-layer` shortcode options but with dots replaced with underscores. If the API is specified in the configuration _and_ the shortcode options, the latter takes precedence. |