Re-organize system-tools.md & improve descriptions

[qiracy]

Description

• Re-organized some sections and added descriptions where they were missing
• Improved a lot of descriptions to solve the same desc annoyance
• Slightly debloated the Wallpapers section by removing some sites that were full of low quality / AI wallpapers, didn't have anything unique or were simply not worth using over something like Wallhaven

Context

It solved the issue of some sections looking inconsistent due to same descriptions for multiple links or no descriptions at all. This change also improves user experience as it'll be easier to figure out whether the wiki has what you're looking for at first glance.

Types of changes

• Bad / Deleted sites removal
• Grammar / Markdown fixes
• Content addition (sites, projects, tools, etc.)
• New Wiki section

Checklist:

• I have read the contribution guide.
• I have made sure to search before making any changes.
• My code follows the code style of this project.