Add gRPC demo site reference to documentation (#2966)

Co-authored-by: fern-api[bot] <115122769+fern-api[bot]@users.noreply.github.com>

Author: devin-ai-integration[bot]

fern/products/api-def/grpc-pages/overview.mdx

@@ -12,7 +12,9 @@ description: gRPC is a high-performance RPC framework that uses Protocol Buffers
 gRPC is a modern, open-source, high-performance Remote Procedure Call (RPC) framework that can run in any environment. It uses Protocol Buffers (protobuf) as the interface definition language and supports multiple programming languages. 
 Fern is compatible with gRPC services and can generate SDKs and documentation from your `.proto` files.
 
-Below is an example of a gRPC service definition: 
+For a working example, see the [gRPC demo docs](https://grpc-demo.docs.buildwithfern.com/) and its [GitHub repository](https://github.com/fern-demo/grpc-demo).
+
+Below is an example of a gRPC service definition:
 
 ```protobuf user_service.proto
 syntax = "proto3";
@@ -230,4 +232,4 @@ fern/
     └─ common.proto
 ```
 </Step>
-</Steps>
+</Steps>