Streamline README for clarity and brevity

[colesmcintosh]

Summary

• Reduce README from 245 to 94 lines (62% smaller)
• Replace verbose operation examples with a table and compact code block
• Consolidate Development/CI/CD/Contributing into one concise section

[github-actions]

👋 Welcome to langchain-salesforce!

Thank you for contributing! Your pull request will be automatically checked for:

• ✅ Code formatting (ruff format)
• ✅ Import sorting (ruff)
• ✅ Linting (ruff check)
• ✅ Type checking (mypy)
• ✅ Spelling (codespell)
• ✅ Unit tests (pytest)

🔍 Required Checks

All pull requests must pass the following checks before merging:

• Pull Request Checks workflow must complete successfully
• All required status checks must be green

🧪 Integration Tests

Integration tests will run automatically on pushes to main. For pull requests, add the integration-tests label to trigger them.

🚀 Getting Started

If you need to fix any issues:

1. Format code: make format
2. Check linting: make lint
3. Run tests: make test

The CI checks will update automatically when you push new commits.

📚 Documentation

• Contributing Guidelines
• Development Setup

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