Improve documentation page

[rizzhal]

This PR improves the documentation page UI of the official Open Printing website. Earlier when I see page the whole page feels like empty and dull.

What I changed -

1. Redesigned the documentation page with a cleaner and more consistent layout
2. Added icons to improve visual representation of documentation sections
3. Improved documentation cards with better spacing, typography, borders, and hover states
4. Improved visual hierarchy and readability across the page etc.

[prisorue]

@rizzhal Amazing work with the icons and the structure of the page! 👏
From my side, the descriptions are reviewed. I've added some suggestions to get ourselves closer to Diataxis.

On the other hand, it's also important to update the headlines so the proposed descriptions fit with the titles; namely:

• 01-printer-application: Overview of printer applications
• 02-designing-printer-drivers: Creating Your First Printer Driver
• 03-designing-scanner-drivers: Scanner driver architecture and guidelines
• 04-packaging-drivers: Packaging and publishing drivers
• 05-User-Manual: Printer application reference

See that I'm suggesting sentence-style for headings, so that proper nouns can be easily identified when mentioned.

[rizzhal]

Thank you @prisorue for your follow up with the suggestions, I am good to go with your suggestions

[rizzhal]

@prisorue fixed with your suggestions