Add info about midddleware in README

Author: ADmad

README.md

@@ -10,6 +10,9 @@
 This plugins provides:
 
 - Route class for generating and matching urls with language prefix.
+- Middleware (dispatcher filter or CakePHP < 3.3) which sets `I18n::locale()`
+  based on language prefix in URL and also provides redirection to appropriate
+  URL with language prefix when accessing site root.
 - Class for retrieving translation messages stored in database instead of po/mo files.
 - Validation class for auto translating validation message.
 - A widget to generate select box with list of timezone identifiers.
@@ -93,6 +96,23 @@ files and populate the translations table. Updating the db records with
 translations for each language is upto you. Having the messages in a table
 instead of files make it much to make a web interface for managing translations.
 
+### I18nMiddleware
+
+You can setup the `I18nMiddleware` in your `src/Application::middleware()` as
+shown:
+
+```php
+$middlware->add(new \ADmad\I18n\Middlware\I18nMiddleware([
+    'defaultLanguage' => 'en',
+    'languages' => [
+        'en' => ['locale' => 'en_US'],
+        'fr' => ['locale' => 'fr_FR']
+    ],
+]));
+```
+
+The keys of `languages` array are the language prefixes you use in your URL.
+
 ### TimezoneWidget
 
 In your `AppView::initialize()` configure the `FormHelper` to use `TimezoneWidget`.