enhancement: enhances the documentation for four fundamental Linux commands echo, su, mkdir, ip (#414)

* Add command documentation for Linux utilities

Added new documentation files for the following commands: ln, systemctl, journalctl, watch, jobs, bg, fg, time, export, ufw, traceroute, and iptables. Updated README.md to include and link to these new command topics, improving coverage and navigation for users seeking information on essential Linux utilities.

* Rename iptables command file and update references

Renamed '148-the-iptables-command.md' to '066-the-iptables-command.md' for consistency. Updated all references in README.md and removed the old '066-the-iptable-command.md' file to correct the filename typo.

* Add new Linux command chapters and update README

Added chapters for cfdisk, badblocks, fsck, mkfs, cpio, lsb_release, dmidecode, apropos, dmesg, !!, tty, and lspci commands. Updated README.md to include these commands in the command lists, tables, and chapter index. Improved formatting and fixed minor formatting inconsistencies throughout the README.

* Rename cfdisk command file and update references

Renamed '148-the-cfdisk-command.md' to '160-the-cfdisk-command.md' and updated all references in README.md accordingly. Also made minor whitespace and formatting corrections in several command documentation files for consistency.

* Rename bangbang command file and update references

Renamed '157-the-!!-command.md' to '157-the-bangbang-command.md' for clarity and updated the README link accordingly. Added a new CSS file for code block highlighting. Updated exported PDF and EPUB files to reflect these changes.

* Expand and improve command documentation

Greatly expanded the documentation for the mkdir, echo, ip, and su commands with detailed usage examples, advanced features, options tables, best practices, troubleshooting, and practical applications. These updates provide comprehensive guidance for users and administrators, replacing brief overviews with in-depth reference material.

* Merge branch 'main' of https://github.com/arsh342/101-linux-commands

Author: arsh342