[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/test_omni_input_preprocessor.py

@@ -1,5 +1,9 @@
+import pytest
+
 from vllm_omni.inputs.preprocess import OmniInputPreprocessor
 
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
 
 def _make_preprocessor(monkeypatch):
     preprocessor = object.__new__(OmniInputPreprocessor)