ENG-7548: update rx.Config docstring (#5752)

* update rx.Config docstring

* update rx.Config docstring

Author: LineIndent

reflex/config.py

@@ -267,24 +267,51 @@ class BaseConfig:
 
 @dataclasses.dataclass(kw_only=True, init=False)
 class Config(BaseConfig):
-    """The config defines runtime settings for the app.
+    """Configuration class for Reflex applications.
 
-    By default, the config is defined in an `rxconfig.py` file in the root of the app.
+    The config defines runtime settings for your app including server ports, database connections,
+    frontend packages, and deployment settings.
+
+    By default, the config is defined in an `rxconfig.py` file in the root of your app:
 
     ```python
     # rxconfig.py
     import reflex as rx
 
     config = rx.Config(
         app_name="myapp",
-        api_url="http://localhost:8000",
+        # Server configuration
+        frontend_port=3000,
+        backend_port=8000,
+        # Database
+        db_url="postgresql://user:pass@localhost:5432/mydb",
+        # Additional frontend packages
+        frontend_packages=["react-icons"],
+        # CORS settings for production
+        cors_allowed_origins=["https://mydomain.com"],
     )
     ```
 
-    Every config value can be overridden by an environment variable with the same name in uppercase and a REFLEX_ prefix.
-    For example, `db_url` can be overridden by setting the `REFLEX_DB_URL` environment variable.
+    ## Environment Variable Overrides
+
+    Any config value can be overridden by setting an environment variable with the `REFLEX_`
+    prefix and the parameter name in uppercase:
+
+    ```bash
+    REFLEX_DB_URL="postgresql://user:pass@localhost/db" reflex run
+    REFLEX_FRONTEND_PORT=3001 reflex run
+    ```
+
+    ## Key Configuration Areas
+
+    - **App Settings**: `app_name`, `loglevel`, `telemetry_enabled`
+    - **Server**: `frontend_port`, `backend_port`, `api_url`, `cors_allowed_origins`
+    - **Database**: `db_url`, `async_db_url`, `redis_url`
+    - **Frontend**: `frontend_packages`, `react_strict_mode`
+    - **State Management**: `state_manager_mode`, `state_auto_setters`
+    - **Plugins**: `plugins`, `disable_plugins`
 
-    See the [configuration](https://reflex.dev/docs/getting-started/configuration/) docs for more info.
+    See the [configuration docs](https://reflex.dev/docs/advanced-onboarding/configuration) for complete details on all available options.
     """
 
     # Track whether the app name has already been validated for this Config instance.