Add API Docs link to README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dadachi

README.md

@@ -8,7 +8,7 @@ The Android version is available here: [NativeAppTemplate-Free-Android](https://
 ## Overview
 
 NativeAppTemplate-Free-iOS is configured to connect to `api.nativeapptemplate.com`.  
-You can purchase the source code for the backend server APIs, made with Ruby on Rails, that power `api.nativeapptemplate.com`:
+You can purchase the source code for the backend server APIs, made with Ruby on Rails, that power `api.nativeapptemplate.com` ([API Docs](https://nativeapptemplate.com/api-docs/index.html)):
 
 - [NativeAppTemplate-API (Solo)](https://nativeapptemplate.com/products/api-solo)  
 - [NativeAppTemplate-API (Team)](https://nativeapptemplate.com/products/api-team)