docs: enhance GitHub Codespaces documentation (#1842)

* docs: enhance GitHub Codespaces documentation

Improved the Codespaces section in README to match the comprehensive
documentation from main branch.

Changes:
- Added detailed "What's Included" section listing pre-installed tools
- Added "Free Tier" information with Student Developer Pack details
- Added new "Cloud Development Environments" section with overview
- Enhanced benefits list with automatic backups mention
- Improved structure with clearer subsections

This provides users with better understanding of what Codespaces offers
and helps them get started more quickly.

* fix: add missing environment key in build-docker-compose.yaml

The CASC_RELOAD_TOKEN environment variable was missing its parent
'environment:' key, causing a YAML parsing error in updatecli.

This was likely introduced when GITPOD_WORKSPACE_URL variables were
removed, leaving the environment section malformed.

Author: gounthar

README.md

@@ -4,19 +4,40 @@ This repository includes the files necessary for transitioning from `docker` to
 
 ### How to Set Up the Repository in GitHub Codespaces? (Recommended)
 
+GitHub Codespaces provides a cloud-based development environment with Docker pre-installed and configured.
+
+#### Quick Start
+1. Click the button below to open this repository in GitHub Codespaces:
+
 [![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/jenkins-docs/quickstart-tutorials)
 
+2. Wait for the Codespace to build (first time: ~2-3 minutes, subsequent starts: ~30 seconds)
+3. Once ready, the setup script will automatically install required tools
+4. Follow the instructions in the terminal to start a tutorial
+
+#### What's Included?
+- Docker and Docker Compose pre-installed
+- `yq` YAML processor for configuration
+- GitHub CLI (`gh`) for repository operations
+- Automatic port forwarding for Jenkins (8080) and applications (3000, 5000)
+- Jenkins URL automatically configured for Codespaces environment
+
+#### Free Tier
+- 60 hours/month for free accounts (sufficient for all tutorials)
+- 120 hours/month with [GitHub Student Developer Pack](https://education.github.com/pack)
+
+## Cloud Development Environments
+
+### GitHub Codespaces
+
+GitHub Codespaces is a cloud-based development environment integrated with GitHub. It provides instant, configured development environments with Docker pre-installed, making it perfect for these Jenkins tutorials.
+
 **Benefits:**
 - No local installation required
 - Consistent environment for all users
 - Free tier: 60 hours/month
 - Accessible from any device with a browser
-
-**Quick Start:**
-1. Click the badge above or the green "Code" button → "Codespaces" tab
-2. Click "Create codespace on main"
-3. Wait for the environment to initialize (~2-3 minutes)
-4. Follow the welcome message in the terminal to start a tutorial
+- Automatic backups via GitHub
 
 ### Steps to Run Examples from the Repository