add logger info

guide/src/qs_10.md

@@ -64,7 +64,9 @@ Active provides several useful middlewares, like *logging*, *user sessions*, etc
 
 Logging is implemented as middleware. 
 It is common to register logging middleware as first middleware for application. 
-Logging middleware has to be registered for each application.
+Logging middleware has to be registered for each application. *Logger* middleware
+uses standard log crate to log information. You should enable logger for *actix_web*
+package to see access log. ([env_logger](https://docs.rs/env_logger/*/env_logger/) or similar)
 
 ### Usage
 
@@ -76,10 +78,14 @@ Default `Logger` could be created with `default` method, it uses the default for
 ```
 ```rust
 # extern crate actix_web;
+extern crate env_logger;
 use actix_web::Application;
 use actix_web::middleware::Logger;
 
 fn main() {
+    std::env::set_var("RUST_LOG", "actix_web=info");
+    env_logger::init();
+
     Application::new()
        .middleware(Logger::default())
        .middleware(Logger::new("%a %{User-Agent}i"))