docs: add walrus php sdk in unofficial sdk list

docs/usage/sdks.md

@@ -8,6 +8,7 @@ Besides these upcoming official SDKs, there also exist unofficial third-party SD
 with the [HTTP API](./web-api.md#http-api-usage) exposed by Walrus aggregators and publishers:
 
 - [Walrus Go SDK](https://github.com/namihq/walrus-go) (maintained by the *Nami Cloud* team)
+- [Walrus PHP SDK](https://github.com/suicore/walrus-sdk-php) (maintained by the *Suicore* team)
 
 Finally, there is [Tusky](https://docs.tusky.io/about/about-tusky), a complete data storage platform
 built on Walrus, including encryption, HTTP APIs, sharing capabilities, and more.