docs: improve contribution guide for local development setup

[e7h4n]

Problem

The current contribution documentation is missing important information for first-time contributors trying to set up the local development environment.

Issues

1. Missing pnpm dev instructions

There are no clear instructions on how to start the development server. Contributors need guidance on the pnpm dev command and where to run it from.

2. Environment variables error on first run

When running the development server for the first time, contributors encounter an error about invalid/missing environment variables:

❌ Invalid environment variables: [{...},{...}]

There should be documentation explaining:

• Which environment variables are required
• How to set up the .env.local file
• Example .env.local.example file or clear instructions

Suggested Improvements

1. Add a "Getting Started" section in the contribution guide with step-by-step instructions
2. Document the pnpm dev command and any prerequisites
3. Explain environment variable setup with examples
4. Consider adding a setup script or improving error messages to guide new contributors

[e7h4n]

consider this after 100 stars