Update documentation for configureAsyncHTTPServerPipeline (#435)

Author: tayloraswift

Sources/NIOHTTP2/HTTP2PipelineHelpers.swift

@@ -579,7 +579,7 @@ extension Channel {
     ///   - http1ConnectionInitializer: An optional callback that will be invoked only when the negotiated protocol
     ///     is HTTP/1.1 to configure the connection channel.
     ///   - http2ConnectionInitializer: An optional callback that will be invoked only when the negotiated protocol
-    ///     is HTTP/2 to configure the connection channel.
+    ///     is HTTP/2 to configure the connection channel. The channel has an ``ChannelOutboundHandler/OutboundIn`` type of ``HTTP2Frame``.
     ///   - http2StreamInitializer: A closure that will be called whenever the remote peer initiates a new stream.
     ///     The output of this closure is the element type of the returned multiplexer
     /// - Returns: An `EventLoopFuture` containing a ``NIOTypedApplicationProtocolNegotiationHandler`` that completes when the channel