fix: update contributing repo URL to termius org

[mervivian]

Summary

CONTRIBUTING.md still points contributors at https://github.com/Crystalnix/hosts-farm/compare/ for opening pull requests, but the repository has since moved to the termius organization (termius/hosts-farm). GitHub currently follows the redirect, but the visible link and organization name in the docs are stale. Updated the PR link to the canonical termius/hosts-farm URL so contributors land on the right compare page directly.

How to reproduce

1. Open CONTRIBUTING.md on master.
2. Scroll to the "submit a pull request" section — the [pr] reference link is https://github.com/Crystalnix/hosts-farm/compare/.
3. Compare with the repo's actual location: https://github.com/termius/hosts-farm.

Test plan

• Read the updated CONTRIBUTING.md and confirm the [pr] reference now points at https://github.com/termius/hosts-farm/compare/.
• Click the "submit a pull request" link in the rendered Markdown and confirm it opens the compare page on termius/hosts-farm without going through a redirect.