Add Openrouter

[JackAdamsJenkins]

Fixes #3

Add Openrouter integration.

• Cargo.toml

  • Add openrouter dependency.

• README.md

  • Add Openrouter setup instructions.
  • Add Openrouter API key to environment variables section.
  • Add Openrouter API key to notes section.

• sample.env

  • Add Openrouter API key environment variable.

• src/main.rs

  • Add OPENROUTER_API_KEY to the list of required environment variables.