URL in section title breaks automatic link

[giuliazanchi]

We noticed that a section heading ### The netplan.io approach was rendered incorrectly on the docs website: there was an automatic link for the section heading + an automatic link for the netplan.io URL-like part.

We fixed it by adding a backslash: ### The netplan\.io approach, but this seems like a bug that needs to be addressed.

The affected page is: How to create an instance