To add pages to the header you just have to set layout:page, rather than post.
There is some some “liquid” code in includes/sidebar.html that looks for all top-level documents classed as “page” and makes sidebar links to the
Create a new file in the top-level/root directory called cv.md.
Paste the following code and commit the new file
---
layout: page
title: CV
---
This is my CV
The header/sidebar should now have a link to your CV
If you want to add a download, i.e. a PDF of your CV, rather than MD file, then don’t add “.md” extension onto the end of your file and it will be a download link.