[ NEW PAGE ] Documenting your ecosystem project

[frankharkins]

Advice for new projects on setting up high-quality documentation. It should cover:

• Setting up Sphinx (maybe also something simpler?)
• Documentation best practices
• qiskit-sphinx-theme

We can base this on https://qisk.it/docs-guide

### Tasks

[abbycross]

Also - @beckykd @abbycross -- help write tips -- couple pphs -- for non-writers doing documentation

[abbycross]

Also - @beckykd @abbycross -- help write tips -- couple pphs -- for non-writers doing documentation

We could at the very least point to https://github.com/Qiskit/documentation/blob/main/style-guide.md

[Eric-Arellano]

The open source section is being inlined into the guides section, so there's no longer a natural place for this.