Improve docs (#225)

Author: hramezani

docs/index.md

@@ -212,12 +212,12 @@ In case of nested models, the `case_sensitive` setting will be applied to all ne
 ```py
 import os
 
-from pydantic import ValidationError
+from pydantic import BaseModel, ValidationError
 
 from pydantic_settings import BaseSettings
 
 
-class RedisSettings(BaseSettings):
+class RedisSettings(BaseModel):
     host: str
     port: int
 
@@ -235,13 +235,10 @@ try:
 except ValidationError as e:
     print(e)
     """
-    2 validation errors for Settings
+    1 validation error for Settings
     redis.host
       Field required [type=missing, input_value={'HOST': 'localhost', 'port': 6379}, input_type=dict]
         For further information visit https://errors.pydantic.dev/2/v/missing
-    redis.HOST
-      Extra inputs are not permitted [type=extra_forbidden, input_value='localhost', input_type=str]
-        For further information visit https://errors.pydantic.dev/2/v/extra_forbidden
     """
 ```
 
@@ -270,6 +267,10 @@ What it does is simply explodes your variable into nested models or dicts.
 So if you define a variable `FOO__BAR__BAZ=123` it will convert it into `FOO={'BAR': {'BAZ': 123}}`
 If you have multiple variables with the same structure they will be merged.
 
+!!! note
+    Sub model has to inherit from `pydantic.BaseModel`, Otherwise `pydantic-settings` will initialize sub model,
+    collects values for sub model fields separately, and you may get unexpected results.
+
 As an example, given the following environment variables:
 ```bash
 # your environment
@@ -315,11 +316,9 @@ print(Settings().model_dump())
 """
 ```
 
-1. Sub model has to inherit from `pydantic.BaseModel`, Otherwise `pydantic-settings` will initialize sub model,
-   collects values for sub model fields separately, and you may get unexpected results.
+1. Sub model has to inherit from `pydantic.BaseModel`.
 
-2. Sub model has to inherit from `pydantic.BaseModel`, Otherwise `pydantic-settings` will initialize sub model,
-   collects values for sub model fields separately, and you may get unexpected results.
+2. Sub model has to inherit from `pydantic.BaseModel`.
 
 `env_nested_delimiter` can be configured via the `model_config` as shown above, or via the
 `_env_nested_delimiter` keyword argument on instantiation.
@@ -460,6 +459,11 @@ class Settings(BaseSettings):
 ```
 
 
+!!! note
+    Pydantic settings loads all the values from dotenv file and passes it to the model, regardless of the model's `env_prefix`.
+    So if you provide extra values in a dotenv file, whether they start with `env_prefix` or not,
+    a `ValidationError` will be raised.
+
 ## Secrets
 
 Placing secret values in files is a common pattern to provide sensitive configuration to an application.