docs: Import common best practices from catalogue

[th3james]

arm/topo-project-catalog#5 introduced some best practices which were actually common enough to belong in this repo. This PR migrates them here.

arm/topo-project-catalog#10 removes the duplication and cross references the new documentation introduced here.

Changes

• Add a new best practices guide
• Update broader documentation to link to best practices at appropriate places
• Update the skills to accordingly
• Add links to the catalogue guidance, but make it clear those are additional requirements specific to the catalogue

Checklist

• 🤖 This change is covered by tests as required.
• 🤹 All required manual testing has been performed.
• 📖 All documentation updates are complete.

[federicobozzini]

We are losing the reference to x-topo.features. Is it intentional?

[th3james]

It was. That feature feels a little bit in flux right now and I didn't want to put too much focus on it at present.

[awphi]

Not 100% it's worth including 'Topo' here - same goes for the existing 'Topo Project Authoring guide though'. Feels like it's implied everything is Topo-related in the docs and 'Project' is already a reserved noun in isolation.

[th3james]

9540fd4