docs: update rugpi instructions to align with rugpi v0.6

[reubenmiller]

Proposed changes

Update rugpi image building instrustions after refactoring the tedge-rugpi-image repo to use new Rugpi features (layers and repositories) introduced in 0.6.

• https://github.com/thin-edge/tedge-rugpi-image (image)
• https://github.com/thin-edge/tedge-rugpi-core (recipes)
• Rugpi release notes: https://oss.silitics.com/rugpi/blog/releases/0.6

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[didier-wenzek]

Not related to the docs, but testing while reading, I got the following error:

$ just build-pi4

Error: loading library

Caused by:
    0: error reading recipe info from path `"/project/recipes/sbom/recipe.toml"
    1: No such file or directory (os error 2)

[didier-wenzek]

"only required for the initial flashing of the device"

I don't fully get this note. This Wifi setting will be used by the device once flashed, not only for the first boot of the image. Isn't it?

[didier-wenzek]

Okay I saw, the note below. The note should be enough.

Suggested change

	4. Optional: Add Wifi ssid/password - only required for the initial flashing of the device
	4. Optional: Add Wifi ssid/password

[reubenmiller]

Removed. Resolved by be3aebc

[didier-wenzek]

Not related to the docs, but testing while reading, I got the following error:

$ just build-pi4

Error: loading library

Caused by:
    0: error reading recipe info from path `"/project/recipes/sbom/recipe.toml"
    1: No such file or directory (os error 2)

This error was unrelated. But because I reused a clone with remaining recipes from the old version.

[didier-wenzek]

Approved

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
390	0	3	390	100	59m12.154999999s