Improve Getting Started Documentation to Reduce Maintenance Burden

[bhouston]

Improve Getting Started Documentation to Reduce Maintenance Burden

This PR addresses issue #29 by improving the platform-specific setup documentation to reduce maintenance burden. The changes link to external resources for installation instructions rather than duplicating them.

Changes Made

macOS Setup Improvements

• Updated Homebrew installation section to link to brew.sh instead of duplicating instructions
• Simplified NVM setup by referring to NVM's official instructions
• Removed specific shell configuration steps that may change over time

Linux Setup Improvements

• Added link to NVM GitHub repository for installation instructions
• Removed duplicated NVM installation steps
• Updated GitHub CLI installation to link to the official page instead of duplicating platform-specific instructions

Windows Setup Improvements

• Moved the NVM for Windows link outside of the code block to make it clickable
• Simplified installation instructions to direct users to the official documentation

Benefits

• Reduces maintenance burden as we won't need to update our docs when third-party tools change their installation procedures
• Ensures users always get the most up-to-date installation instructions
• Maintains focus on MyCoder-specific setup while delegating standard tool installations to their respective maintainers

Testing

• Verified all links are functional and point to the correct resources
• Built the documentation locally to ensure proper rendering
• Ensured all MyCoder-specific instructions are preserved