docs: add CLI usage and development workflow documentation

[CoolatMax]

Description

This PR adds missing CLI documentation for Nanoforge and provides a clear “how to use it” guide that shows every step required to develop a game correctly using the CLI.

The documentation is workflow-first and includes both a step-by-step development guide and a structured CLI command reference.

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What is the type of issue?

Documentation was missing.

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What is the issue?

The existing documentation did not contain sufficient information about how to use the Nanoforge CLI, including:

• The correct order of commands for development
• How to use the CLI end-to-end
• How CLI commands relate to the game development workflow

This made it difficult for new users to develop a game without inspecting the source code.

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What was added in this PR?

• A complete “how to use it” guide describing every step to develop a game correctly:
  1. Creating a new project
  2. Starting the development environment
  3. Developing the game
  4. Building the project for production
• A structured CLI command reference covering:
  • nf new
  • nf start
  • nf build
  • nf generate
  • nf install add
• Accurate documentation for CLI options, aligned with the current CLI implementation

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Where did you find it?

The missing documentation was identified while reviewing the existing docs/ content and comparing it against the available CLI commands and development workflow.

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Scope

• Documentation-only changes
• No changes to CLI behavior or source code

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Related issue

Closes #41