Merge pull request bunq#97 from bunq/update-sandbox-api-key-procedure

Update Sandbox API key procedure. (bunq#96)

README.md

@@ -10,7 +10,7 @@ Now you can build even bigger and better apps and integrate them with your bank
 
 Before you dive into this brand new SDK, please consider:
 - Checking out our new developer’s page [https://bunq.com/en/developer](https://bunq.com/en/developer) 🙌  
-- Grabbing your production API key from the bunq app or asking our support for a Sandbox API key 🗝
+- Grabbing your production API key from the bunq app or generate a Sandbox API key using [Tinker](https://www.bunq.com/developer) 🗝
 - Visiting [together.bunq.com](https://together.bunq.com) where you can share your creations,
 questions and experience 🎤