Add Netty links

Author: nicktindall

docs/internal/GeneralArchitectureGuide.md

@@ -54,8 +54,8 @@ that require [operator privileges], populate the [audit logs] and perform some a
 HTTP traffic is handled by an implementation of a [HttpServerTransport]. The `HttpServerTransport` is responsible for binding to a
 port, handling REST client connections, parsing received requests into [RestRequest] instances and dispatching those
 requests to a [HttpServerTransport.Dispatcher]. The [RestController] is an implementation of `HttpServerTransport.Dispatcher`.
-The `HttpServerTransport` is pluggable. There is only a single [Netty-based implementation][Netty4HttpServerTransport]
-of `HttpServerTransport`, but some plugins, such as `Security`, supply instances of it with
+The `HttpServerTransport` is pluggable. There is a single [Netty](https://netty.io/)-based implementation
+of `HttpServerTransport`, the [Netty4HttpServerTransport], but some plugins, such as `Security`, supply instances of it with
 additional configuration to implement features like IP filtering or TLS (see [Security#getHttpTransports]).
 
 [ActionModule#initRestHandlers]:https://github.com/elastic/elasticsearch/blob/v9.0.1/server/src/main/java/org/elasticsearch/action/ActionModule.java#L814
@@ -151,7 +151,7 @@ to register interceptors by implementing the [getTransportInterceptors][NetworkP
 
 The transport infrastructure is pluggable and implementations can be provided by [NetworkPlugin#getTransports]. The role of the [Transport]
 is to establish connections between nodes over which [TransportRequest]s can be sent, maintain a registry of [TransportRequestHandler]s for
-routing inbound requests and maintain state to correlate inbound responses with the original requests. There is a single Netty-based TCP
+routing inbound requests and maintain state to correlate inbound responses with the original requests. There is a single [Netty](https://netty.io/)-based TCP
 transport used in production Elasticsearch, the [Netty4Transport], but the security plugin extends that to add SSL and IP filtering
 capabilities.