fix: Update Zap integration link in README (#253)

Author: just1and0

README.md

@@ -113,7 +113,7 @@ const Checkout = () => {
 - ✅ Fully typed params for transactions
 - ✅ Works seamlessly with Expo & bare React Native
 - ✅ Full test coverage
-- ✅ Zap integration
+- ✅ [Zap](https://paystack.com/zap) integration
 
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