Classroom: Docker installation is the real setup barrier

[cuihtlauac]

Parent issue: #24

Problem (from UCSD study, Valstar et al., ITiCSE 2020)

In a 416-student study, 18% found DevContainer setup difficult and 35% needed help. The authors pinpoint the cause: installing Docker itself is the hard part, not the devcontainer. Once Docker works, opening the devcontainer is "a single mouse click."

64% of TAs agreed they "had to help many students with setting up their DevContainer." The authors argue this is a one-time cost that only occurs in the first course using DevContainers.

Historical issues included Windows Home edition lacking Hyper-V support (now resolved by WSL2, but WSL2 setup itself can be a friction point).

Proposed changes

• Create a docs/setup-guide.md with platform-specific Docker installation instructions:
  • Windows: WSL2 + Docker Desktop (note: WSL2 must be enabled first)
  • macOS: Docker Desktop (Intel vs Apple Silicon)
  • Linux: Docker Engine (avoid snap package, prefer apt)
• Include a verification step: docker run hello-world
• Link to the guide from the main README
• Include common troubleshooting (Docker daemon not running, WSL2 not enabled, insufficient disk space)