Code and explanation issues

This commit adds a more detailed explanation of the computed properties snippet. I was really confused when I saw that, so I filled out the explanation and added a link to the Ember guides.

The other piece of code on this commit changes the code on looping through the users from

    <td>{{#linkTo 'users.show' user}}{{user.fullName}}{{/linkTo}}</td>

to

    <td>{{#linkTo 'users.show' this}}{{fullName}}{{/linkTo}}</td>

I'm not sure where the top one (originally in the post) came from. That code makes Ember throw an error. I had to change mine to the updated version by reading Stack Overflow. Before this commit, I checked the app repo, and it actually uses the same line as in this commit. So I'm not sure if the original line is from a previous release candidate or something, and the repo was updated, but not the post? Either way, this code works.

Also removed a few whitespace errors.