doc: fix stale README config examples and field references

[Copilot]

Description

The README had two stale areas: path was documented as a per-scanner field inside [kics] and [opengrep], but the actual Config struct and both scanner factories use a single top-level path field. The proxy example block also omitted ssl_cert_file.

Changes:

• Config TOML example — moved path out of [kics] and [opengrep] to the top level; removed redundant # Directory to scan comments from scanner sections
• Proxy example block — added missing ssl_cert_file line to the commented-out proxy snippet
• Fields Reference table — replaced the two separate [kics].path / [opengrep].path rows with a single top-level path row; updated footnote to reflect both scanners share it

# Before: path was duplicated inside each scanner section
[kics]
path = "./my-service"
...
[opengrep]
path = "./my-service"

# After: single top-level field, matching the actual Config struct
path = "./my-service"
[kics]
...
[opengrep]

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that causes existing functionality to change)
• Documentation update
• Refactor / code cleanup
• CI / build change

How Has This Been Tested?

Documentation-only change. Verified against loader/dto.go (Config.Path top-level field) and both scanner factories (kics/factory.go, opengrep/factory.go) which consume config.Path.

Checklist

• My code follows the project's coding standards (go vet ./... passes)
• I have run the existing test suite and all tests pass (go test ./...)
• I have added or updated tests that cover my changes
• I have updated documentation where relevant (README, comments, etc.)
• I have not introduced new secrets, credentials, or sensitive data
• My changes do not break backward compatibility (or I have documented breaking changes above)

Screenshots / Output (if applicable)

N/A