docs: add resource recommendation for charm deployment

[florentianayuwono]

Applicable spec:

Overview

Add the following recommendation for openstack flavor:

• 2 vCPUs
• 8 GiB RAM
• 20 GiB disk

which is the superset of the requirements stated in the code:

MIN_CPU = 2
MIN_RAM = 1024 # M
MIN_DISK = 20 # G

and existing README guidance:

You'll need a working OpenStack installation with
flavors with a minimum of 2 CPU cores, 8GB RAM and 10GB disk.

Rationale

So that user knows the recommended resource for deploying image builder and doesn't run into issues.

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, senior-review-required, documentation)
• The docs/changelog.md is updated with user-relevant changes in the format of keep a changelog v1.1.0
• The application version is incremented in app/pyproject.toml

[Copilot]

Pull request overview

Adds clearer OpenStack flavor sizing guidance (recommended vs minimum) for deploying/running the GitHub runner image builder, aligning documentation with the minimums enforced by the OpenStack builder logic.

Changes:

• Updated README prerequisites to list recommended and minimum accepted builder VM resources.
• Added a “Recommended resources” section to the charm quick-start tutorial.
• Added a similar resources recommendation to the CLI quick-start tutorial.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
README.md	Adds recommended and minimum accepted OpenStack flavor sizing for the builder VM.
docs/tutorial/quick-start.md	Documents recommended builder VM flavor resources and references build-flavor.
app/doc/tutorial/quick-start.md	Adds recommended OpenStack flavor sizing guidance for CLI-driven builds.

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