Docs: add model dump guide

docs/usage/rest-api.md

@@ -217,6 +217,40 @@ resp: Response[FullRepository] = github.rest.repos.get("owner", "repo")
 repo: dict[str, Any] = resp.json()
 ```
 
+=== "Pydantic v1"
+
+    If you have already got the parsed data and want to dump it into a dict object or JSON string, you can use the pydantic model's `dict` or `json` method:
+
+    ```python hl_lines="8-9"
+    from typing import Any
+    from githubkit import Response
+    from githubkit.versions.latest.models import FullRepository
+
+    resp: Response[FullRepository] = github.rest.repos.get("owner", "repo")
+    repo: FullRepository = resp.parsed_data
+
+    repo_dict: dict[str, Any] = repo.dict(by_alias=True, exclude_unset=True)
+    repo_json: str = repo.json(by_alias=True, exclude_unset=True)
+    ```
+
+=== "Pydantic v2"
+
+    If you have already got the parsed data and want to dump it into a dict object or JSON string, you can use the pydantic model's `model_dump` or `model_dump_json` method:
+
+    ```python hl_lines="8-11"
+    from typing import Any
+    from githubkit import Response
+    from githubkit.versions.latest.models import FullRepository
+
+    resp: Response[FullRepository] = github.rest.repos.get("owner", "repo")
+    repo: FullRepository = resp.parsed_data
+
+    repo_dict: dict[str, Any] = repo.model_dump(
+        mode="json", by_alias=True, exclude_unset=True
+    )
+    repo_json: str = repo.model_dump_json(by_alias=True, exclude_unset=True)
+    ```
+
 ## REST API Versioning
 
 githubkit supports multiple versions of GitHub API, you can switch between versions as follows: