Improve README structure and clarity

[doramirdor]

This PR improves the README to make it more compelling and easier to understand for first-time visitors.

Changes

Added sections:

• Hero section - Clear problem/solution framing at the top
• How It Works - 5-step workflow showing the full cycle
• Why Alma? - Comparison table vs Linear/Jira/GitHub Projects
• Who Should Use Alma? - Clear fit/no-fit guidance
• Roadmap - Future plans and priorities

Improvements:

• Reordered sections for better flow (hero → how → why → demo → who)
• Added context to Demo section (explains what you're seeing)
• Clarified value prop before diving into technical details
• Fixed minor typo ("everything runs in-process" instead of "— everything")

Why these changes?

The current README jumps straight to the demo without answering:

• What problem does this solve?
• Why would I use this over Linear/Jira?
• Who is this for?

This PR addresses those questions upfront, making it easier for developers to quickly evaluate whether Alma fits their workflow.

Preview

The new structure:

1. Title + tagline
2. Problem statement
3. How it works (5 steps)
4. Comparison table
5. Demo (with context)
6. Who should use this
7. (existing content: screenshots, tech stack, setup, etc.)
8. Roadmap

All existing content is preserved, just reorganized for clarity.