Update README.md

[DevMatei]

This pull request includes several updates to the README.md file to improve its clarity, structure, and readability. The changes involve rephrasing descriptions, adding sections, and formatting enhancements.

Key changes include:

Content Updates:

• Rephrased the description of Pop!_OS to be more concise and engaging.

Structural Enhancements:

• Added sections for "First Release," "Official Website," and "Pop!_OS Documentation."
• Updated the "Purpose" section to provide a clearer explanation of the repository's role.

Formatting Improvements:

• Introduced horizontal rules (---) to separate sections for better readability.
• Reformatted the list of available scripts to include descriptions and proper markdown formatting.

Developer Resources:

• Separated instructions for building the shell into a dedicated "Building the Shell" section.
• Added a "Developer Communication" section with a link to the development chat.

Contribution Guidelines:

• Moved the contribution instructions to a new "Contributing" section for better visibility.