update lpic: less doc

Linux/LPIC1/13-less.md

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+# 📘 **Using `less` in Linux/Unix**
+
+`less` is a terminal pager program used to view the content of files one screen at a time. It's especially useful for viewing large files or logs.
+
+---
+
+## 📂 Basic Usage
+
+```bash
+less file
+```
+
+**Description**:
+Opens `file` for viewing.
+
+```bash
+less /var/log/syslog
+```
+
+**Description**:
+Opens the system log file for reading. Useful for examining system logs line by line.
+
+---
+
+## ⌨️ Common Keyboard Shortcuts
+
+Here are the most frequently used keyboard shortcuts when using `less`:
+
+| Key/Command | Action                               |
+| ----------- | ------------------------------------ |
+| `space`     | Scroll **down** one screen           |
+| `b`         | Scroll **up** one screen             |
+| `q`         | **Quit** `less`                      |
+| `/pattern`  | **Search** forward for `pattern`     |
+| `n`         | Go to the **next** match of pattern  |
+| `N`         | Go to the **previous** match         |
+| `g`         | Go to the **first line** of the file |
+| `G`         | Go to the **last line** of the file  |
+
+---
+
+## ✅ Summary
+
+`less` is a vital tool for system administrators, developers, and anyone dealing with large text files. With simple navigation and powerful search capabilities, it makes file reading efficient and user-friendly.
+