docs: add Kotlin example for API_GetUserGameLeaderboards (#89)

Author: official-wizard

docs/v1/get-user-game-leaderboards.md

@@ -54,6 +54,27 @@ const gameLeaderboards = await getUserGameLeaderboards(authorization, {
 });
 ```
 
+```kotlin [Kotlin]
+val credentials = RetroCredentials("<username>", "<web api key>")
+val api: RetroInterface = RetroClient(credentials).api
+
+val response: NetworkResponse<GetUserGameLeaderboard.Response, ErrorResponse> = api.getUserGameLeaderboards(
+    gameId = 14402,
+)
+
+if (response is NetworkResponse.Success) {
+    // handle the data
+    val leaderboard: GetUserGameLeaderboard.Response = response.body
+
+} else if (response is NetworkResponse.Error) {
+    // if the server returns an error it be found here
+    val errorResponse: ErrorResponse? = response.body
+
+    // if the api (locally) had an internal error, it'll be found here
+    val internalError: Throwable? = response.error
+}
+```
+
 :::
 
 ## Response