Fetching data via jquery and adding items to a list
Your code looks good, and I'm not going to suggest comestic changes. However:


the_url is not informative enough, try to find a variable that conveys that this url will let you fetch the repositories of an user.
Did you consider that repo.name could contain a ' which would cause you to output wrong html? Fortunately, GitHub prevents such things to happen.
Declare var i; at the top of your success function. Here's why.
The way you're building your html string is dangerous.  It's also hard to read and easy to get wrong.

As Philip suggested, using some sort of template would be a good idea, but there's no way to do this in standard jQuery (jQuery templates have been deprecated, and the way forward seems to be JsRender which is not yet Beta). Fortunately, your code is not big enough for you to need that. Instead, use attr(), text() and addClass() wisely:

var dt = $('&lt;dt&gt;').attr('href', repo.url).attr('title', repo.name).text(repo.name);
var dd = $('&lt;dd&gt;').addClass('project-description').text(repo.description);
$('#gh-projects').append(dt).append(dd);