Docs Guidelines: clarify qiskit vs beyond qiskit strategy

[javabster]

We should organise some discussion around the strategy for documentation in terms of a strategy for Qiskit Terra docs and non-qiksit-terra docs.

We should cover the following questions in our discussions:

• Is the chimera project only covering Qiskit Terra? Or should we also plan to integrate applications modules etc into qiskit.org?
• What are the branding requirements for docs for different qiskit adjacent packages?
• What are the long term plans for the sphinx theme? Should we still maintain the sphinx theme for use by the broader qiskit ecosystem? Who should maintain the theme?
• What parts of documentation should we be actively involved in maintaining, and which should we just provide guidelines for? e.g. terra tutorials - do we actively maintain or just advise?

Definition of Done:

• A page in the docs guidelines and internal open source wiki that explains the strategy and addresses the above questions

[javabster]

Expanding this issue to discuss the following:

• what should the sphinx theme look like for ecosystem members - is there different branding? should we have ecosystem/tier criteria for who can use the qiskit sphinx theme and branding?
• should we have a different top menu for qiskit.org and ecosystem projects?

[Eric-Arellano]

This has had some progress. We now have the technology for different Sphinx "theme variants": #229

What remains is figuring out how exactly the ecosystem theme should be different, which is tracked by #311.