added the nl command chapter with details and examples.

[thesmartdeveloperr]

What type of PR is this? (check all applicable)

• [ ] ♻️ Refactor
• [ x] ✨ New Chapter
• [ ] 🐛 Bug Fix/Typo
• [ ] 👷 Optimization
• [ ] 📝 Documentation Update
• [ ] 🚩 Other

Description

added the nl command which is really useful for text manipulation and editing.

Added to documentation?

• [ ] 📜 readme
• [ ] 🙅 no documentation needed

[optional] What gif best describes this PR or how it makes you feel?

[thesmartdeveloperr]

@bobbyiliev pls review and let me know if anything has to be changed.