docs: upgrade README for show the new feature

The "new feature" refers to the possibility of adding the controllers
one by one to the FastAPI instances and the need to inherit from an
APIController base class.

README.md

@@ -23,8 +23,14 @@ pip install fastapi-control
 
 ```python
 from fastapi import FastAPI
-
-from fastapi_control import add_controllers, controller, get, inject
+from fastapi_control import (
+    APIController,
+    add_controller,
+    add_controllers,
+    controller,
+    get,
+    inject,
+)
 
 
 # Optionally declares an abstraction
@@ -61,10 +67,11 @@ class NestedGretterImplementation:
         return self.gretter.greet()
 
 
-# With the @controller decorator, we can declare class-based routing (also
-# called controller) and it has the same parameters as FastAPI's APIRouter
+# With the @controller decorator and inheriting from APIController, we can
+# declare class-based routing (also called controller) and it has the same
+# parameters as FastAPI's APIRouter
 @controller(prefix="/home")
-class HomeController:
+class HomeController(APIController):
     # When the @controller decorator is used, the arguments of the __init__
     # method are automatically injected (if the @inject decorator was used
     # in the argument type declarations)
@@ -97,6 +104,12 @@ class HomeController:
 api = FastAPI()
 # Finally, it is necessary to add the controllers to the FastAPI instance
 add_controllers(api)
+
+# If you want to have multiple FastAPI instances with different controllers,
+# you can use the add_controller method to add the desired controllers to
+# the desired FastAPI instance one by one.
+other_api = FastAPI()
+add_controller(other_api, HomeController)
 ```
 
 ## Inspirations