Provide some guidance on how one can become a core developer and explain
the different types of contribution one can make.

Signed-off-by: Stephen Finucane <stephen@that.guru>

- Replace unicode quotes with ascii, since Sphinx will automatically
  translate these for us
- Move the header to the root document
- Use an admonition instead of a header for the attribution section

Signed-off-by: Stephen Finucane <stephen@that.guru>

Reorder this to flow a little better and re-add the CONTRIBUTING
document, which now simply points to the main documentation.

Signed-off-by: Stephen Finucane <stephen@that.guru>

This completes the migration from the CONTRIBUTING document to the new
in-tree contributing guide. The CONTRIBUTING document itself is
temporarily removed so that git will correctly mark the document as
having been moved. A future change will re-add this document as well as
rework the new contributing document.

Signed-off-by: Stephen Finucane <stephen@that.guru>

This is based on content extracted from the CONTRIBUTING document.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Provide an introduction to how the Sphinx team is organized. This will
be expanded upon in a future change.

Signed-off-by: Stephen Finucane <stephen@that.guru>

This is modelled off Django's guide of the same name [1]. In summary,
this will contain most of the information previously found in the
CONTRIBUTING document. For now, we move just the code of conduct and
authors documents.

Signed-off-by: Stephen Finucane <stephen@that.guru>