chore: add php sdk link to docs

Author: omer-topal

docs/api-reference/introduction.mdx

@@ -29,6 +29,7 @@ Permify exposes its APIs via both [gRPC](https://buf.build/permifyco/permify/doc
 - [Java](https://github.com/Permify/permify-java)
 - [Javascript](https://github.com/Permify/permify-javascript)
 - [Typescript](https://github.com/Permify/permify-typescript)
+- [PHP](https://github.com/Permify/permify-php/)
 
 
 <Note>