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.