Add cross-platform development setup documentation

[parthdagia05]

Documentation: Cross-Platform Development & Source Setup Guide

Closes #12

Overview

Currently, the project documentation primarily covers the Windows .exe installation workflow. This PR introduces comprehensive guides for setting up and running MUIO from source on macOS, Linux, and Windows, reducing onboarding friction for new contributors and research teams.

---

What’s New?

1. Dedicated Development Setup Page

Created docs/source/getting-started/dev-setup.rst which provides step-by-step instructions for:

• macOS Setup: Homebrew installation for GLPK and CBC (including Apple Silicon paths).
• Linux/Ubuntu Setup: APT-based installation and dependency management.
• Windows (Source): Alternative workflow for developers not using the pre-compiled .exe.
• Environment Configuration: Guidance on using MUIO_GLPK_PATH and MUIO_CBC_PATH environment variables.

2. Technical Deep-Dives

Added documentation for previously "hidden" logic discovered in the codebase:

• Solver Auto-Discovery: How the system identifies binaries via the system $PATH.
• Encoding Notes: Guidance on handling the UTF-16LE encoding in requirements.txt.
• Permissions: Documentation on DATA_STORAGE directory permissions (0o777) required for successful execution.

3. Improved Discoverability

• Updated docs/source/index.rst to include the new guide in the main Table of Contents.
• Added a "Development (Run from Source)" section to the root README.md to point users directly to the full documentation.

---

Impact & Risk

• Zero Runtime Risk: This PR contains only .rst and .md files. No functional code is modified.
• Backward Compatibility: Does not affect existing build pipelines or the Windows release workflow.

---

Checklist

• Documentation follows the existing Sphinx/RST style.
• All internal links and toctree references are functional.
• Verified that the documentation builds locally without warnings.
• README links point correctly to the new sections.

---

[parthdagia05]

@VedranKapor can you review this.