docs: address review comment

Author: dkhawk

README.md

@@ -95,6 +95,7 @@ Full guides for using the utilities are published in
 
 ## Usage
 
+<details>
   <summary>Marker utilities</summary>
 
 ### Marker utilities
@@ -103,6 +104,7 @@ Full guides for using the utilities are published in
 - Marker clustering [source](https://github.com/googlemaps/android-maps-utils/tree/main/library/src/main/java/com/google/maps/android/clustering), [guide](https://developers.google.com/maps/documentation/android-sdk/utility/marker-clustering)
 - Advanced Markers clustering [source](https://github.com/googlemaps/android-maps-utils/tree/main/library/src/main/java/com/google/maps/android/clustering), [sample code](https://github.com/googlemaps/android-maps-utils/blob/main/demo/src/main/java/com/google/maps/android/utils/demo/CustomAdvancedMarkerClusteringDemoActivity.java)
 - Marker icons [source](https://github.com/googlemaps/android-maps-utils/blob/main/library/src/main/java/com/google/maps/android/ui/IconGenerator.java), [sample code](https://github.com/googlemaps/android-maps-utils/blob/main/demo/src/main/java/com/google/maps/android/utils/demo/IconGeneratorDemoActivity.java)
+</details>
 
 <details>
   <summary>Data visualization utilities</summary>