Add questions to the FAQ

[garrett]

• Blank page: Incorrect time (display blank ,after login cockpit#17995)
• Machines not working as expected: EFI/BIOS settings for VM not enabled (Unsuccessfully run of any SO on cockpit-machines cockpit-machines#879)
• Dark mode autodetection not working? We have a workaround in the switcher, but it might be good to have a pointer to the details I added in the blog post about it.
• Changing the port of Cockpit
• Communicating with us on IRC?
• Reporting bugs?

Some of these are duplicates (with ? at the end) to other documentation on the website, it's probably good to have pointers to those from the FAQ too.