Added myself to contributors

[JaapvanEkris]

What this changes

Added myself to the list of contributors

Class of change

Tick one. If you are unsure between two, tick the heavier.

• [X ] Editorial — typo, formatting, or wording that changes no requirement
• Substantive — new or changed field, changed conformance requirement,
  changed compliance level. Requires a linked proposal.
• Structural — governance, licensing, repository scope
• Repository plumbing only — templates, CI, docs about the process

Does any existing conforming file become non-conforming, or change meaning?

• [X ] No
• Yes — described below

Existing files in the wild are the main constraint on this project, and a change
that quietly invalidates them is the one failure mode with no remedy. If yes,
say what breaks and for whom.

Checklist

• One logical change — no unrelated fixes bundled in
• Paragraphs I did not change are not reflowed (keeps the diff readable)
• registry/field-ids.md updated, if any field ID
  is touched
• Linked issue closed or updated, if this resolves one
• RFC 2119 keywords are deliberate, and state producer and consumer
  obligations separately where they differ
• Version number in spec/FIT_STANDARD.md not changed — versions are
  assigned at release
• Implementation evidence linked, for anything that changes file contents