Add classes to nav links
Add classes to nav links

This is to allow tweaking these links via CSS

Signed-off-by: Rohan Jain <f3a935f2cb7c3d75d1446a19169b923809d6e623@gmail.com>

yeefom/cocoa-hugo-theme,lpancescu/cocoa-hugo-theme,nishanths/cocoa-hugo-theme