chore: update pydantic v2 usage in readme (0b01001001#331)

Signed-off-by: Keming <kemingy94@gmail.com>

README.md

@@ -13,7 +13,8 @@ Yet another library to generate OpenAPI documents and validate requests & respon
 
 * Less boilerplate code, only annotations, no need for YAML :sparkles:
 * Generate API document with [Redoc UI](https://github.com/Redocly/redoc) or [Swagger UI](https://github.com/swagger-api/swagger-ui) :yum:
-* Validate query, JSON data, response data with [pydantic](https://github.com/samuelcolvin/pydantic/) :wink: (we support both v1 and v2)
+* Validate query, JSON data, response data with [pydantic](https://github.com/samuelcolvin/pydantic/) :wink:
+  * If you're using Pydantic V2, you will need to import the `BaseModel` from `pydantic.v1` to make it compatible
 * Current support:
   * Flask [demo](#flask)
   * Quart [demo](#quart)