Improve comm_gemm_overlap documentation and HuggingFace integration guidance

[sbhavani]

The comm_gemm_overlap example needs clearer documentation on:

1. How to enable GEMM+communication overlap - The process (initialize userbuffers, set layer flags, cleanup) should be explicitly documented with minimal code snippets
2. Layer-specific parameters - Clarify the difference between ub_tp_comm_overlap vs individual flags
3. Hugging Face integration - Provide guidance on combining with HF model replacement patterns

Current state:
examples/pytorch/comm_gemm_overlap/README.md covers requirements and run commands but lacks setup guidance