docs: add environment variables configuration guide

[melihaltin]

Summary

Added a comprehensive environment variables configuration section to CONTRIBUTING.md to help new contributors set up their development environment more easily. This includes step-by-step instructions for generating security keys, configuring AI model APIs, and setting up OAuth integrations for GitHub and Google services.

Fixes #(issue)

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other: ___________

Testing

✅ Tested on macOS:

• Verified all OpenSSL commands work correctly
• Confirmed OAuth callback URLs format matches the codebase
• Tested that all environment variable names align with existing .env.example
• Validated markdown formatting renders properly

Reviewers should focus on:

• Accuracy of the OAuth setup instructions
• Completeness of required vs optional environment variables
• Clarity of step-by-step instructions for new contributors

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (N/A for documentation)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Screenshots/Videos

Before: Contributors had no clear guidance on environment setup
After: Clear step-by-step environment configuration guide with:

• Security key generation commands
• AI model API key options (OpenAI, Anthropic, Ollama)
• GitHub and Google OAuth setup instructions
• Required vs optional variable distinction

[vercel]

@melihaltin is attempting to deploy a commit to the Sim Team on Vercel.

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[greptile-apps]

Greptile Summary

This PR adds a comprehensive environment variables configuration section to the CONTRIBUTING.md file to help new contributors set up their development environment. The new documentation section provides step-by-step instructions for copying the .env.example file, generating security keys using OpenSSL, and configuring essential environment variables including database connections, authentication settings, and API keys for various services.

The addition fills a significant gap in the contributor onboarding process by providing clear guidance on environment setup, which previously required contributors to piece together information from multiple sources. The documentation follows a logical structure, progressing from required core variables to optional AI model APIs and OAuth integrations for GitHub and Google services. This change integrates well with the existing CONTRIBUTING.md structure and complements the existing .env.example template by providing actionable setup instructions.

PR Description Notes:

• Contains Turkish comments in the issue reference section
• References a non-specific issue number placeholder

Confidence score: 2/5

• This PR contains several critical inaccuracies that could mislead new contributors and cause setup failures
• Score reflects significant discrepancies between documented variables and actual .env.example requirements, plus incorrect file path instructions
• Pay close attention to the environment variables configuration section for accuracy verification against the actual codebase

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