docs: streamline community benchmark intake

[AIwork4me]

Summary

• update the README hero to reflect tested gfx1100 and gfx1151 configurations without turning tested evidence into a generic support claim
• add a GitHub Issue Form for independent AMD GPU / ROCm benchmark submissions
• keep contributor intake aligned with the existing immutable-evidence workflow

Community benchmark intake

The new form captures:

• hardware and GPU architecture
• OS / kernel / ROCm / HIP
• MinerU and exact model revision
• backend/version/runtime details
• benchmark identity and result counts
• Overall and supporting metrics
• patches / architecture overrides
• prediction-manifest integrity
• immutable public evidence

Raw predictions remain optional.

Contributors do not assign verified status or central platform-review outcomes.

Validation

• pytest: 177 passed
• scripts/check_repo.py: clean
• ROCmDoc conformance: CONFORMANT
• Issue Form YAML parse: passed
• git diff --cached --check: passed

Related community example: #21