Add PHP bindings to the list of related projects

Author: dosten

README.md

@@ -76,3 +76,4 @@ libgraphqlparser is BSD-licensed. We also provide an additional patent grant.
 - [graphql-parser (Ruby interface)](https://github.com/Shopify/graphql-parser)
 - [py-graphqlparser (Python interface)](https://github.com/elastic-coders/py-graphqlparser)
 - [graphql_parser (Elixir interface)](https://github.com/aarvay/graphql_parser)
+- [graphql-parser-php (PHP interface)](https://github.com/dosten/graphql-parser-php)