docs: Add GitHub Actions usage documentation to README

[Copilot]

Added documentation for running debos in GitHub Actions workflows using the official container with KVM support.

Changes

• Added new "Using debos in GitHub Actions" section after Docker installation section in README.md
• Includes complete workflow example demonstrating:
  • Container configuration with KVM device passthrough (--device=/dev/kvm)
  • Using ghcr.io/go-debos/debos:main image
  • Example build step with --fakemachine-backend=kvm
• Documents key configuration requirements for ubuntu-latest runners

jobs:
  build:
    runs-on: ubuntu-latest
    container:
      image: ghcr.io/go-debos/debos:main
      options: --device=/dev/kvm
    steps: 
      - uses: actions/checkout@v4
      - run: debos --fakemachine-backend=kvm --print-recipe recipe.yaml

Original prompt

Add GitHub Actions usage documentation to README

Add a new section to the README.md that documents how to use debos in GitHub Actions workflows. This section should be placed after the "Installation (Docker container)" section.

The documentation should focus on the recommended approach: using the official debos container with KVM support on GitHub's ubuntu-latest runners.

Changes needed:

Add the following section after line 84 (after "See docker/README.md for usage."):

## Using debos in GitHub Actions

debos can be run in GitHub Actions using the official container with KVM support
for isolated and reproducible builds:

```yaml
jobs:
  build:
    runs-on: ubuntu-latest
    container:
      image: ghcr.io/go-debos/debos:main
      options: --device=/dev/kvm
    steps: 
      - uses: actions/checkout@v4
      - run: debos --fakemachine-backend=kvm --print-recipe recipe.yaml

Key points:

• GitHub's ubuntu-latest runners have KVM support
• The --device=/dev/kvm option provides KVM access to the container
• debos will use fakemachine with KVM for isolated builds
• Use --print-recipe to see the final recipe after template expansion

This provides users with a simple, working example of how to integrate debos into their CI/CD pipelines using the recommended KVM-based approach.

This pull request was created from Copilot chat.

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