feat: improve content-relationship help text

[angeloashmore]

Resolves: #98

Description

Improve the --help output for field add content-relationship to clearly explain:

• Content relationships are for data fetching, not navigation
• How --custom-type and --tag filtering works
• The downstream impact of changing field constraints

Checklist

• A comprehensive Linear ticket, providing sufficient context and details to facilitate the review of the PR, is linked to the PR.
• If my changes require tests, I added them.
• If my changes affect backward compatibility, it has been discussed.
• If my changes require an update to the CONTRIBUTING.md guide, I updated it.

Preview

How to QA ¹

prismic field add content-relationship --help
prismic field add --help

🤖 Generated with Claude Code

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Note

Low Risk
Help/CLI description text only; no behavioral changes to field creation logic or data handling.

Overview
Updates the prismic field add content-relationship help text to more clearly describe intended usage (data fetching vs navigation) and how --tag/--custom-type restrict selectable documents.

Also adjusts option and subcommand descriptions in field-add to match the clarified guidance; no runtime behavior changes.

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