doc: Add comprehensive README documentation for cm tool

[Copilot]

Overview

This PR adds comprehensive documentation to the README.md file, providing clear setup instructions and complete reference documentation for the cm (course management) tool.

Changes

The README has been completely rewritten from a 3-line placeholder to a focused 204-line guide that includes:

Key Sections Added

1. Installation - Simple installation instructions using go install

2. Prerequisites - Required tools (Go 1.24+, GitHub CLI) for working with the cm tool

3. Initial Setup - Two-step workflow:

   • Creating environment configuration with cm init-env
   • Initializing course repositories with cm init-repos

4. Common Workflows - Real-world examples for:

   • Setting up a new course
   • Managing student repositories
   • Generating course materials

5. Environment Variables - Complete reference table documenting all variables (YEAR, COURSE, NAME, COURSE_ORG, BOT_USER, DISCORD_JOIN_URL)

6. Repository Structure - Visual representation of the expected directory layout

7. Available Commands - Full reference of all cm commands with descriptions

8. Troubleshooting - Solutions for common issues including GitHub authentication, missing .env file, permission issues, and tool version problems

Content Sources

All documentation content is derived from existing code:

• Command descriptions from main.go and doc.go
• Environment variable details from init_env.go

Design Decisions

• The documentation focuses exclusively on the cm tool itself
• Does not assume any particular workflow or integration approach (e.g., Justfile)
• Courses can integrate cm in whatever way suits their needs
• The repository includes an example Justfile for courses that want to use that approach

Verification

• All tests continue to pass
• Tool builds successfully
• All referenced commands have been verified to exist
• Documentation accurately reflects the current state of the tool

Original prompt

---

This section details on the original issue you should resolve

<issue_title>doc: add documentation to the readme</issue_title>
<issue_description>- [ ] Explain that you need to set GOPRIVATE

• Run the various just commands to set up and install stuff.</issue_description>

<agent_instructions>Create README.md with better documentation. See doc.go file for additional details.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #17

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[meling]

Apply changes throughout the file, based on my provided comments.

[meling]

I've made the repository public, so we can remove the GOPRIVATE related stuff.

[Copilot]

Removed all GOPRIVATE references throughout the README. Commit: 1dc266a

[meling]

1.24

[Copilot]

Updated Go version to 1.24. Commit: 1dc266a

[meling]

This section is misleading. The Justfile is included here only as an example for courses to use alongside the cm tool.

[meling]

I prefer that this readme only refers to the cm tool, documenting its usages, not how it is used from the Justfile. Courses may chose other ways to use cm, and this readme should be the documentation for it.

[Copilot]

Refocused README to document the cm tool exclusively. Removed Quick Start section and "Using Just Commands" section. The documentation now focuses on cm commands only, with no assumptions about how courses use it. Commit: 1dc266a

[Copilot]

Apply changes throughout the file, based on my provided comments.

Applied all changes based on the review comments:

• Removed GOPRIVATE references (repository is now public)
• Updated Go version to 1.24
• Removed Just/Justfile documentation to focus solely on the cm tool
  Commit: 1dc266a