[FEATURE] 📚 Improve Project Setup Documentation and Environment Variables Guide

# 📚 Improve Project Setup Documentation

## Problem
The current README lacks comprehensive setup instructions, making it difficult for new contributors to get the project running locally. Missing information about environment variables, database setup, and development workflow.

## Current Issues
- No clear environment variables documentation
- Missing database setup instructions
- No step-by-step development guide
- Lack of troubleshooting section
- No information about required API keys

## Proposed Solution

### 1. **Environment Variables Documentation**
Create a comprehensive `.env.example` file and document all required variables:
- Database connection string
- GitHub API token
- Clerk authentication keys
- Other service configurations

### 2. **Setup Guide**
Add detailed setup instructions including:
- Prerequisites (Node.js, Go, PostgreSQL)
- Database initialization
- Frontend setup (Next.js)
- Backend setup (Go crawler/updater)
- Running the development environment

### 3. **Development Workflow**
Document the development process:
- How to run the crawler
- How to start the frontend
- How to make changes and test
- How to contribute code

### 4. **Troubleshooting Section**
Add common issues and solutions:
- Database connection problems
- API rate limiting
- Build errors
- Environment setup issues

## Benefits
- **For new contributors**: Easier onboarding process
- **For maintainers**: Less time spent helping with setup issues
- **For the project**: More contributors can get started quickly
- **For the community**: Better developer experience

## How to Contribute

### For Documentation Writers:
- Create comprehensive setup guides
- Write troubleshooting documentation
- Improve README structure

### For Developers:
- Create `.env.example` files
- Add setup scripts
- Document API requirements

### For DevOps:
- Create Docker setup (optional)
- Add CI/CD documentation
- Document deployment process

## Implementation
Can be implemented in phases:
1. Environment variables documentation
2. Basic setup guide
3. Advanced troubleshooting

## Labels
- `documentation`
- `good first issue`
- `setup`
- `beginner-friendly`