There is a short story titled "The Witcher", is included as a bonus material, and its give some background to one of the main plot of the first game.

There is a short story that, if I remember correctly, was collected in the first Witcher book (which was a collection of short stories). Trying to go through the entire series first can be a bit of a pain, since I am not entirely sure that all of them have been translated, and the ones that have been criticized by some for their translations. That said, I read the first book, and it didn't blatantly come across as poorly translated, and it provides far more background than you need.

Bought the game, downloaded the story file tried reading, didn't find it that interesting or well written, i hope this is not an important factor for immersion for this game :o

*because as a student reading is something i find myself fairly burnt out on and i have a hard time finnishing uninteresting books etc :o

No, it's not necessary to read it to understand the game.