Update main README with dual-audience approach

[Thinkersbluff]

Update root README.md to serve both 3D printer owners and developers.

Tasks:

• PRIMARY SECTION: Clear path for 3D printer owners
  • "I just want firmware" quick start
  • Download links and basic flashing instructions
  • Hardware compatibility checker
  • Common troubleshooting (friendly language)
• SECONDARY SECTION: Developer and contributor information
  • Link to detailed build documentation
  • Repository structure explanation
  • Contribution guidelines
• TERTIARY SECTION: Repository organization (for reference)

Acceptance Criteria:

• README serves both user types effectively
• All links work correctly
• New users can follow setup instructions
• Professional appearance maintained

Dependencies: Move documentation files
Estimate: 4 story points

[Thinkersbluff]

Accidentally created - cleaning up