[arch-general] Instructions to mount efivars as readonly should be linked to in Beginner's Guide

[Jayesh Badwaik]

Hi,

I have read the dangers of mounting efivars as writable recently, and I think 
there should be an entry in the archlinux installation guide and beginner's 
guide which should say exactly what is said in the warning in [1], and then 
link to [1] for further instructions. 

-- 
Cheers
Jayesh Badwaik

[1] https://wiki.archlinux.org/index.php/
Unified_Extensible_Firmware_Interface#Mount_efivarfs