Fix Custom Endpoint example (#577)

Author: IAmSurajBobade

www/docs/pages/transports/http.mdx

@@ -367,7 +367,7 @@ func main() {
     mux := http.NewServeMux()
 
     // Add MCP endpoints
-    server.AddMCPRoutes(mux, s, "/mcp")
+    mux.Handle("/mcp", server.NewStreamableHTTPServer(s))
 
     // Add custom endpoints
     mux.HandleFunc("/api/status", handleStatus)
@@ -693,4 +693,4 @@ The headers are automatically populated by the transport layer and are available
 
 - **[In-Process Transport](/transports/inprocess)** - Learn about embedded scenarios
 - **[Client Development](/clients)** - Build MCP clients for HTTP transport
-- **[Server Basics](/servers/basics)** - Review fundamental server concepts
+- **[Server Basics](/servers/basics)** - Review fundamental server concepts