Add "next" and "previous" buttons

[erikeckhardt]

While I did figure out how to navigate to the next part of the tutorial by clicking on the next item in the menu on the left, I did waste some time looking around for how to get to the next step, and wasn't 100% certain at first whether the menu at the left really did go to the next item. (In some web sites, a menu on the left might jump whole chapters instead of go to the next content item.) Consider adding "next" and "previous" buttons.

[steveambielli]

I also questioned myself if whether or not I reached the end of the lesson. If there was a "Next" button it would have indicated to me that I completed that lesson and able to move on.

[levibotelho]

Yup sounds like a good idea.