Add a Known Calamares Issues section to the Installer page

[TraceyC77]

Known issues for Calamares
These are upstream issues that will need to be resolved by the Calamares project.

• Bootloader not installed when using custom partitioning on a BIOS system.
  Workaround: Use automatic partitioning and set up manual partitioning after system is installed.
  On systems with UEFI available, use that instead of BIOS.

• When starting without an Internet connection, after "waiting for modules", you may see "The system is not connected to the Internet" with a tooltip "is connected to the Internet."

• When starting Calamraes without an Internet connection, the language is set to English(US) and the timezone is New York, regardless of your selected language / region.
  Workaround: Set these manually.

[TraceyC77]

I'll do this after the website update, to minimize churn