Improve clarity, restructure intro, and streamline installation instructions

[ghost]

This pull request updates the README.md to improve clarity, organization, and accessibility for new users. The changes focus on restructuring the introduction, updating installation instructions, and cleaning up outdated or redundant information.

Documentation improvements:

• Reorganized the introduction by moving the project description into a dedicated "What is Rare?" section and updating the logo/header formatting for better readability.
• Removed outdated Debian-based installation instructions and notes about optional packages, streamlining the installation section.

Installation instructions:

• Commented out the step for installing dependencies with requirements.txt and provided guidance for installing additional features and FreeBSD support in comments, making the instructions less cluttered for most users. [1] [2]

Accessibility:

• Added a Discord shield badge directly under the logo for easier access to community support.

[ghost]

I am waiting for help with the part about building from source.

Actually, I added command wrote in #589.

[ghost]

I also removed DUR, as it doesn't work with "make deb" either.

[loathingKernel]

Thank you, this looks fine to me as it is. I am fine with DUR being removed, the Debian/Ubuntu ecosystem doesn't have the necessary versions of the dependencies last time I looked into it.

The FreeBSD section can be removed too, since Rare doesn't use Qt5/PyQt5 any more but rather pyside6.

[loathingKernel]

Thank you again, merged.