📝 Fix dead Ariadne FastAPI docs link in How To - GraphQL

The linked page https://ariadnegraphql.org/docs/fastapi-integration now
returns 404; Ariadne removed their /docs/ tree. Repoint the "docs for
FastAPI" link to the current canonical Ariadne resource, the project
repository at https://github.com/mirumee/ariadne, whose README documents
its ASGI/FastAPI integration. This is also where ariadnegraphql.org now
links for documentation.

docs/en/docs/how-to/graphql.md

@@ -21,7 +21,7 @@ Here are some of the **GraphQL** libraries that have **ASGI** support. You could
 * [Strawberry](https://strawberry.rocks/) 🍓
     * With [docs for FastAPI](https://strawberry.rocks/docs/integrations/fastapi)
 * [Ariadne](https://ariadnegraphql.org/)
-    * With [docs for FastAPI](https://ariadnegraphql.org/docs/fastapi-integration)
+    * With [docs for FastAPI](https://github.com/mirumee/ariadne)
 * [Tartiflette](https://tartiflette.io/)
     * With [Tartiflette ASGI](https://tartiflette.github.io/tartiflette-asgi/) to provide ASGI integration
 * [Graphene](https://graphene-python.org/)