Add SQA-oriented operations and troubleshooting guidance to README

[Copilot]

artdaq’s Moderate SQA classification requires user-facing documentation for basic operation and common failure modes. This PR adds concise operational guidance and a troubleshooting section in the main README, aligned with existing artdaq-demo onboarding.

• What was added

  • New “Basic operation (SQA)” section in README.md:
    • points users to artdaq-demo as the primary getting-started path
    • documents the standard run lifecycle (environment setup → process start with FHiCL → run-control transitions → log review)
  • New “Common errors and troubleshooting (SQA)” section:
    • missing environment/library setup
    • invalid FHiCL configuration
    • transfer/network connectivity issues
    • stale shared-memory resources after abnormal termination
    • art process startup/runtime failures with PMT/MessageFacility log triage guidance

• Documentation shape

  • Keeps guidance at operator level (symptoms + actions), without introducing implementation-specific internals.
  • Extends existing README structure rather than adding new docs files.

## Common errors and troubleshooting (SQA)

* **Invalid FHiCL configuration**  
  Symptoms include configuration parsing exceptions or process failure during initialization.  
  Action: validate FHiCL syntax/parameter names and retry with corrected configuration.