PS Beginner Guide update

I changed the Pokemon Showdown Forum link to match the Pokemon Showdown Forums on Smogon. It seems most logical, since the listed resources have been moved there instead now. I also included 'News' on the list of resources/links, as they contain relevant information about Pokemon Showdown.
Merge pull request #509 from smogon/1ab1fc419b41d2ee2493a2092a753cdf

PS Beginner Guide update