docs: describe immune response data format

[SufianTA]

Summary

• document the expected file layout for custom immune-response cohorts
• list the patient-table and query CSV columns reflected by the bundled IMVigor210 examples
• clarify how --patient-tpm-root relates to per-patient TPM files

Validation

• git diff --check
• python -m compileall -q medea main.py setup.py

Addresses #9