Add 'ls' command to list available project templates

[mythz]

Features:

• List all templates from NetCoreTemplates and NetFrameworkTemplates
• List templates from a specific organization: npx create-net ls
• Display templates in 2-column format: name and description
• Fetch data from GitHub API with proper error handling
• Sort repositories by last updated
• Bold section headers and formatted output

Command usage:
npx create-net ls # List all default templates
npx create-net ls NetFrameworkTemplates # List specific org templates

Implementation:

• Add fetchJSON() function to retrieve data from GitHub API
• Add listTemplates() function with optional organization parameter
• Update help text to include ls command
• Handle both 'ls' and 'list' commands
• Graceful error handling for network issues

Documentation:

• Update README with ls command examples
• Add Commands section to README
• Show usage examples for both listing and creating