Improve documentation

[kiwichick888]

I find it so frustrating trying to learn something about a qBt feature only to find there's no documentation for it. For example: Search Engine and Torrent Creator. As far as I can see, neither of those are even mentioned in the wiki docs, let alone have any instructions on how to use them. If you're providing the features, please provide some kind of documentation for them (even just mentioning they exist would be a help).