Add CamerPay PHP SDK to E-commerce section

CamerPay is a payment gateway focused on Cameroon supporting Mobile Money
(Orange Money, MTN MoMo), credit cards (Visa, Mastercard via Stripe) and
PayPal. The official PHP SDK ships with zero runtime dependencies (native
cURL), typed exceptions per HTTP status code, and HMAC-SHA256 webhook
verification using hash_equals() for timing-attack safety.

- Repository: https://github.com/camerpay/php-sdk
- Packagist:  https://packagist.org/packages/camerpay/php-sdk
- License:    MIT
- Requires:   PHP 8.1+
- Tagged release: v1.0.0
- Documentation: https://camerpay.biz/docs

README.md

 
 * [Money](https://github.com/moneyphp/money) - A PHP implementation of Fowler's money pattern.
 * [Brick Money](https://github.com/brick/money) - A money library for PHP, with support for contexts, cash roundings, currency conversion.
+* [CamerPay PHP SDK](https://github.com/camerpay/php-sdk) - Official PHP SDK for CamerPay payment gateway (Mobile Money, cards, PayPal) in Cameroon.
 * [OmniPay](https://github.com/thephpleague/omnipay) - A framework agnostic multi-gateway payment processing library.
 * [Payum](https://github.com/payum/payum) - A payment abstraction library.
 * [Shopsys Framework](https://github.com/shopsys/shopsys/) - An open source e-commerce platform for in-house development teams.