Some useful links were also added

Added some useful links that we saw that may help people improving their gameplay. While we don't help people with builds directly, we give advice and it may be good to test them theoretically at some calculators to later try them in the battlefield.
If someone thinks that a link should be there, post it and give us a reason. If we see it worth to have it listed, we will add it.

We have also our first guide about a class near done. We will make it about the PVP Assassin Cross.