add kernel downgrade instructions

arch.md

@@ -443,10 +443,22 @@ alias lmt='ls -t -1'
 
 ### Downgrading Kernel
 
+You can find old kernel versions at <https://archive.archlinux.org/packages/l/linux/>
+
+You can find old kernel-header versions at <https://archive.archlinux.org/packages/l/linux-headers/>
+
+If you want to downgrade to a previously installed kernel you can use pacman cache:
+
 1. `cd /var/cache/pacman/pkg`
 2. `pacman -U linux-x.x.x.arch1-1-x86_64.pkg.tar.zst linux-headers-x.x.x.arch1-1-x86_64.pkg.tar.zst`
 3. `reboot`
 
+If you want to downgrade to a kernel that wasn't previously installed:
+
+1. Download linux... and linux-headers... from above
+2. `pacman -U linux-x.x.x.arch1-1-x86_64.pkg.tar.zst linux-headers-x.x.x.arch1-1-x86_64.pkg.tar.zst`
+3. `reboot`
+
 ## Packages
 
 ### Official