`gel instance restore` is undocumented

https://docs.geldata.com/reference/using/cli/gel_instance

`gel instance restore` does not appear in the list at the above link, nor does it have its own page

Unsurprisingly, the bot also doesn't know about it

It is however mentionned in point 3 of https://docs.geldata.com/learn/localdev#undoing-destructive-changes
