Add installation instructions to README and the docs

[PeterDaveHello]

Add a dedicated installation page covering pip, pipx, source install, upgrade, and verification. Link it from the docs index and Quick Start, and expose requirements and install commands in the README for easier onboarding.

Close #849

GitHub Copilot summary:

This pull request updates the documentation to provide clearer installation instructions and improve the onboarding experience for new users. The most significant changes are the addition of a dedicated installation guide, updates to the quick start workflow, and improvements to the README to make requirements and setup steps more prominent.

Installation and setup documentation:

• Added a new docs/source/installation.rst file with comprehensive installation instructions, including prerequisites, installation methods (pip, pipx, source), upgrade steps, and verification.
• Linked the new installation guide in the documentation table of contents by adding installation to the docs/source/index.rst toctree.

README improvements:

• Expanded the README.md with sections for Features, Requirements, Installation, Quick start, and Documentation, making it easier for users to get started and understand the project’s capabilities.
• Removed a blank line near the top of README.md for formatting consistency.

Quick start workflow:

• Updated the introduction in docs/source/introduction.rst to reference the new installation guide and clarify the initial setup steps.