Add PracticeLinux to Wargames section

Hi, I'd like to suggest adding [PracticeLinux](https://www.practicelinux.com) to the **Wargames** section.

It's a browser-based Linux training platform that uses CTF-style challenges to teach terminal skills. No installation required and no account needed to start. You get a real isolated Linux environment directly in the browser and hunt for flags using actual commands.

It fits well alongside OverTheWire and similar wargames as an entry point, particularly for people who want to build Linux muscle memory before tackling more advanced platforms.

**Suggested entry:**
`[PracticeLinux](https://www.practicelinux.com) - Browser-based CTF challenges for learning Linux hands-on with no setup required.`

Happy to open a PR if that's preferred.

Open the repository's Wargames section and compare its existing entry format. Add the provided PracticeLinux link and description in the appropriate list position, then review the rendered Markdown to confirm the link and wording display correctly.

Written by the indexing model from the issue text.