docs: add Kotlin example for API_GetGameProgression (#90)

Co-authored-by: Wes Copeland <[email protected]>

Author: official-wizard

docs/v1/get-game-progression.md

@@ -20,6 +20,33 @@ A call to this endpoint will retrieve information about the average time to unlo
 | `i`  | Yes       | The target game ID.                                                       |
 | `h`  |           | 1 to prefer players with more hardcore unlocks than non-hardcore unlocks. |
 
+## Client Library
+
+::: code-group
+
+```kotlin [Kotlin]
+val credentials = RetroCredentials("<username>", "<web api key>")
+val api: RetroInterface = RetroClient(credentials).api
+
+val response: NetworkResponse<GetGameProgression.Response, ErrorResponse> = api.getGameProgression(
+    gameId = 228,
+)
+
+if (response is NetworkResponse.Success) {
+    // handle the data
+    val gameProgression: GetGameProgression.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
 
 ::: code-group