docs: add nilsreichardt as a contributor for security

[allcontributors]

Adds @nilsreichardt as a contributor for security.

This was requested by iluwatar in this comment

[skip ci]

[github-actions]

PR Summary

Registers nilsreichardt as a security contributor in the All Contributors configuration and updates the README to reflect the new contributor, including badge count and the table entry.

Changes

File	Summary
.all-contributorsrc	Added a new contributor entry for nilsreichardt with name Nils Reichardt, avatar URL, profile, and a security contribution in the contributors list.
README.md	Updated All Contributors badge count from 392 to 393 and added nilsreichardt to the contributors table with a security contribution.

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autogenerated by presubmit.ai

[github-actions]

✅ LGTM!

Review Summary

Commits Considered (2)

• 379efcb: docs: update .all-contributorsrc [skip ci]
• 52594f2: docs: update README.md [skip ci]

Files Processed (2)

• .all-contributorsrc (1 hunk)
• README.md (2 hunks)

Actionable Comments (0)

Skipped Comments (3)

• .all-contributorsrc [3578-3587]

  maintainability: "Add new security contributor entry."

• README.md [9-9]

  best_practice: "Update All Contributors badge count"

• README.md [586-586]

  maintainability: "Add new contributor to README contributors table"