Sync config example in sonata_overview

[mgeplf]

• to include the populations dictionary
• enable intersphinx
• fix tox compat

[jdcourcol]

I am good. I have no clue about the tox thing so I will let @GianlucaFicarelli comment on that.

[mgeplf]

LGTM, but I wonder why intersphinx is needed?

I'm planning on linking snap doc to here, if it works out.