[CI] Add pytest markers to current tests and update the doc. (#577)

Signed-off-by: Alicia <115451386+congw729@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/entrypoints/openai_api/test_serving_chat_sampling_params.py

@@ -11,6 +11,8 @@ from unittest.mock import MagicMock
 import pytest
 from vllm.sampling_params import SamplingParams
 
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
 
 @pytest.fixture
 def mock_comprehension_stage():