docs: add help text for amass metadata

[Nairayadav]

Fixes #522

Changes

• Added help text for the Root Domain field in plugins/amass/metadata.json
• Clarified the expected input format for Amass subdomain enumeration
• Refreshed the plugin checksum

Verification

• Updated metadata successfully
• Refreshed checksum using scripts/refresh_plugin_checksum.py
• Verified JSON structure remains valid

[utksh1]

Backend tests are failing, so this cannot merge yet. Please rebase on latest main, regenerate the amass metadata checksum from the current plugin files, and make sure the parser output contract/backend test suite passes before requesting another review.

[Nairayadav]

Thanks for the review.

I rebased the branch on the latest main and regenerated the checksum.

While investigating the CI failure, I found an inconsistency in the local validation tooling:

• python scripts/refresh_plugin_checksum.py --plugin amass reports the checksum is already up to date.
• python scripts/validate_plugins.py passes for all plugins, including amass.
• python scripts/validate_plugin.py --plugin amass reports a checksum mismatch.

The PR only adds the requested help text and updates the checksum. Since the validators are producing conflicting results, the parser contract failure may be related to the current plugin validation/loading logic rather than the metadata change itself.

Could you advise whether there is an additional checksum regeneration or plugin registration step expected after the recent plugin checksum rollout changes?

[utksh1]

Re-reviewed the latest push. Backend integration is still failing. Please keep this to amass help text only, avoid icon/format churn, refresh the checksum with the repo script, rebase on main, and rerun checks.

[utksh1]

Approved after maintainer cleanup. The PR is now focused on plugin field help text and the affected plugin checksum validates locally.