docs: update readme and plugin guides

guides/plugin/readme.md

@@ -50,6 +50,19 @@ Plugins.register(:my_custom_plugin, MyCustomPlugin)
 
 To load and use a plugin in your Lennarb application, call the plugin method in your application class.
 
+```ruby
+Lennarb.new do |app|
+	app.plugin :my_custom_plugin
+
+	app.get '/custom' do |req, res|
+		res.status = 200
+		res.html(custom_method)
+	end
+end
+```
+
+And if you are using the `Lennarb::Application::Base` class, you can use the `plugin` method directly in your application class.
+
 ```ruby
 class MyApp < Lennarb::Application::Base
   plugin :my_custom_plugin

readme.md

@@ -40,6 +40,8 @@ Plese see [Performance](https://aristotelesbr.github.io/lennarb/guides/performan
 
   - [Performance](https://aristotelesbr.github.io/lennarb/guides/performance/index.html) - The **Lennarb** is very fast. The following benchmarks were performed on a MacBook Pro (Retina, 13-inch, Early 2013) with 2,7 GHz Intel Core i7 and 8 GB 1867 MHz DDR3. Based on [jeremyevans/r10k](https://github.com/jeremyevans/r10k) using the following [template build](static/r10k/build/lennarb.rb).
 
+  - [Plugin](https://aristotelesbr.github.io/lennarb/guides/plugin/index.html) - You can create your plugins to extend the functionality of the framework.
+
   - [Response](https://aristotelesbr.github.io/lennarb/guides/response/index.html) - This is the response guide.
     The `res` object is used to send a response to the client. The Lennarb use a custom response object to send responses to the client. The `res` object is an instance of `Lennarb::Response`.