You can add it in the form of Static site pages. These can also be external links.
For adding a site page go to Manage >content> click on pages
And click on add new page.
You can add to types of Site pages.
a) Page Content - This is the page on which you can write your own content.
b) Redirect to a link - In this case, you can provide an external link of the page.
and click to save and upload.