docs: improve README readability and value proposition

[tony]

This commit overhauls the README to make it more skimmable and immediately valuable to new users:

• Add clear value proposition at the top to immediately communicate purpose and benefits
• Create 'Why Use libvcs?' section with emoji-highlighted bullet points for key features
• Reorganize examples into 'Quick Examples' section that appears earlier in the document
• Add helpful comments to doctests to explain their purpose
• Restructure content with improved headings, spacing, and visual separators
• Convert the 'Core Features' section to a numbered list for better hierarchy
• Create dedicated 'Documentation & Resources' and 'API References' sections
• Streamline the entire document for better discoverability and readability
• Keep all doctests functional (4 passing tests, up from 3 previously)

The goal is to make the value of libvcs immediately apparent to new visitors while maintaining a clean document structure that's easy to navigate.

Summary by Sourcery

Improve the README to enhance readability and provide a clearer value proposition for new users. The changes include adding a value proposition, reorganizing examples, improving content structure, and adding documentation and API references.

Enhancements:

• Restructure the README content for improved readability and discoverability.
• Reorganize examples into a 'Quick Examples' section that appears earlier in the document.
• Convert the 'Core Features' section to a numbered list for better hierarchy.
• Add helpful comments to doctests to explain their purpose.
• Create dedicated 'Documentation & Resources' and 'API References' sections.
• Streamline the entire document with improved headings, spacing, and visual separators.
• Add a 'Why Use libvcs?' section with emoji-highlighted bullet points for key features.
• Add a clear value proposition at the top to immediately communicate purpose and benefits.