Sword of Destiny (Brokilon) is absolutely necessary.Absolutely start with The Last Wish, and then Sword of Destiny. I'll admit. The Last Wish is kind of a drag, as are the first few stories of Sword of Destiny. But they're kind of important to knowing who's who and what's going on in the world. Absolutely do not start with Time of Contempt. Blood of Elves is the first book in the mainline series and it picks up immediately after Sword of Destiny.
I suppose, if you really wanted to, you could skip The Last Wish as a whole and just read parts of it. The stories in it that are absolutely essential are "A Question of Price" and "The Last Wish". The rest aren't super necessary.
It's where we meet Ciri for the first time