Add development documentation for repository cloning and setup

[Copilot]

The README lacked instructions for developers wanting to clone and contribute to the project.

Changes

• Development section with complete workflow:
  • Repository cloning instructions
  • Environment setup using uv with security notes and alternative installation methods
  • Package build process with python -m build
  • Testing setup (pytest installation + note on infrastructure status)
  • Code quality tooling (black, ruff, mypy)
  • Basic contribution workflow

Example

Developers can now follow:

# Clone and setup
git clone https://github.com/kaleab-ayenew/vity.git
cd vity

# Install uv (with security verification note)
curl -LsSf https://astral.sh/uv/install.sh | sh

# Setup environment
uv venv && source .venv/bin/activate
uv pip install -e ".[dev]"

# Build
uv pip install build
python -m build

Consistent package manager usage (uv) throughout all instructions.

Original prompt

how do I create a new repo that is a clone of an existing repo

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