docs: add term style guide

[kmishra1204]

Closes #20.

Summary

• Adds docs/term-style-guide.md for candidate term writing, one-line disambiguators, aliases, related/contrasting terms, scope notes, category selection, and working group attribution.
• Links the guide from the repository structure table in README.md.
• Keeps the change limited to taxonomy style guidance and does not add candidate taxonomy terms.

Scope note

Issue #12 asks delegates not to open PRs for candidate terms yet. This PR respects that boundary by adding contribution guidance only, so future term drafts can be prepared consistently before full taxonomy entries are submitted.

Validation

• git diff --check
• ASCII scan for README.md and docs/term-style-guide.md
• Confirmed referenced files exist: CONTRIBUTING.md, docs/data-schemas.md, and taxonomy/taxonomy-data.js

[kmishra1204]

Validated this current head after fetching upstream main.

Local checks:

• Branch is one commit ahead and zero behind upstream main
• git diff --check origin/main...fork/codex/term-style-guide-issue-20
• Changed-file scope is markdown-only: docs/term-style-guide.md, README.md
• Relative links in changed markdown resolve inside the branch
• No TODO/FIXME/example placeholder text found in changed files