Issuing a build warning if the user has secure boot enabled but…

[FNGarvin]

Thanks for your fantastic software! I did not think the dongle would EVER be supported. Great to finally feel like it's no longer necessary to recommend the 360 dongle after all these years.

Your use of dkms is perfect, but the way that the software will silently create new self-signed keys can be a bit of a gotcha to someone using secure boot (eg, https://www.reddit.com/r/linux_gaming/comments/1as5tos/xone_doesnt_work/). It's beyond the scope of this project to dive deep on security, but it is IMHO appropriate to at least offer some breadcrumbs.

To that end, I have added a build warning for the case that a user has secure boot enabled but doesn't yet have keys in the default locations (eg, someone coming from akmods). I've also added a small blurb to the troubleshooting section of the README giving an overview of what this might mean and what to do. I believe these changes could be invaluable to novice and intermediate users until such time as your wonderful package becomes canonized by distros or the kernel itself.

Cheers!