docs: add Bun installation option

[AchintyaAshok]

Summary

• document bunx usage to install hypertool-mcp alongside npx
• note bun install docs

Testing

• npm test (fails: Server not built. Run 'npm run build' first.)
• npm test -- --reporter=dot (fails: Server not built. Run 'npm run build' first.)

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https://chatgpt.com/codex/tasks/task_b_68baff51fadc83309534e77eee8f9bf3

[github-actions]

🤖 Changeset Status

⚠️ No changeset found - This PR will default to patch version when merged.

Is this the right version bump?

• 🐛 Bug fixes, small improvements → Automatic patch is perfect! ✅
• ✨ New features, API additions → Consider adding a minor changeset
• 💥 Breaking changes → Please add a major changeset

How to add a changeset:

1. Run npx changeset in your terminal
2. Select the appropriate version bump (patch/minor/major)
3. Write a short description of your changes
4. Commit the generated .changeset/*.md file

Skip release entirely:

Add [skip-ci] to your PR title if this shouldn't trigger any release.

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