Shane Jekyll Portfolio Theme has a custom navigation option. You can create navigation easily there.
At first open the the file _data/navigation.yml file

Here following the navigation code structure :

- text: Home
  url: home
- text: About
  url: about
- text: Portfolio
  url: portfolio
- text: News
  url: news
- text: Contact
  url: contact

You can use any custom URL there and also text can be change there.