Update middlewares doc

docs/middlewares.md

@@ -1,6 +1,28 @@
 # Middlewares
 
-You can create your own middlewares by inheriting from ```HTTP::Handler```
+## Built-in Middlewares
+
+Kemal has built-in middlewares for common use cases.
+
+### HTTP Basic Authorization
+
+This middleware let's you add HTTP Basic Authorization support to your Kemal application.
+To increase easy of use you can use this middleware with `basic_auth` macro like below.
+
+```crystal
+require "kemal"
+
+basic_auth "username", "password"
+
+get "/" do
+  "This won't render without correct username and password."
+end
+
+```
+
+## Custom middlewares
+
+You can create your own middleware by inheriting from ```HTTP::Handler```
 
 ```crystal
 class CustomHandler < HTTP::Handler