Adding a new item to the main menu?

Hello Forum. On my site at greenland-fishery.org.uk, the main menu only shows the categories I've set to show (Whales, Walrii etc). But I want to add an About Us link.

How to do that, please? And I've tried hard-wiring it into menu.twig and that hasn't worked... yet

Did you try this?
https://www.antropy.co.uk/blog/how-to-c ... t-3-0-2-0/