Most dynamic content management systems (e.g. WordPress allows you to easily build tag and category pages that assist in navigation of your site, and add some Google juice.
Unfortunately this isn't so easy if you want to host a static site on Github Pages.... It's 100% possible if you are generating the site locally and pushing to Github, but unfortunately you can't use Ruby plugins with Github pages.
However, lucky for us, it is possible to hack together a bit of a solution using straight Liquid tags. You can get a whole tags page going that links internally, you just can't generate individual tag pages for each tag. Can't have it all I suppose.
There is a live example up on my site at the tag page.