How to create navigation entry that is just a link?

I am sorry if this seems to be a stupid question, but I could not find an answer in the Grav documentation:

How do I create a navigation/menu entry that is just a link to another website?

My Grav website only consists of a single page in a multi-language setup, and I just want to add a navigation entry that links to another website. Since the navigation is generated from available pages, that would mean creating a new page that really is just a link, so how can that be done?

See the TwentyFifteen theme, for example, which inserts links from site.yaml at the end of the autogenerated navigation.

Some themes use that approach (Antimatter, Deliver..) which is just a convention, nothing "built into Grav" but an example of using the configuration.

I'm looking for an easy solution that can be done with the Grav admin. I have just discovered a "Page redirect" option in the Page Editor (Advanced) tab at the Overrides section, that is not explained in the Grav documentation:

Grav

Is that what I am looking for and how does it work exactly?