secure boot: fix typos, add inline code formatting

Signed-off-by: Alexander Zeidler <a.zeidler@proxmox.com>

system-booting.adoc

@@ -380,10 +380,11 @@ and integration in `proxmox-boot-tool`.
 
 The following packages need to be installed for Secure Boot to be enabled:
 
-- shim-signed (shim bootloader signed by Microsoft)
-- shim-helpers-amd64-signed (fallback bootloader and MOKManager, signed by Proxmox)
-- grub-efi-amd64-signed (Grub EFI bootloader, signed by Proxmox)
-- proxmox-kernel-6.X.Y-Z-pve-signed (Kernel image, signed by Proxmox)
+- `shim-signed` (shim bootloader signed by Microsoft)
+- `shim-helpers-amd64-signed` (fallback bootloader and MOKManager, signed by
+  Proxmox)
+- `grub-efi-amd64-signed` (Grub EFI bootloader, signed by Proxmox)
+- `proxmox-kernel-6.X.Y-Z-pve-signed` (Kernel image, signed by Proxmox)
 
 Only Grub as bootloader is supported out of the box, since there are no other
 pre-signed bootloader packages available. Any new installation of {pve} will
@@ -419,7 +420,7 @@ To check the latter, run:
 # findmnt /
 ----
 
-If the host is indeed running using ZFS as root filesystem, the `FSTYPE` column
+If the host is indeed using ZFS as root filesystem, the `FSTYPE` column
 should contain `zfs`:
 ----
 TARGET SOURCE           FSTYPE OPTIONS
@@ -485,8 +486,8 @@ can try adding it manually (if supported by the firmware), by adding the file
 
 NOTE: Some UEFI firmwares are known to drop the `proxmox` boot option on reboot.
 This can happen if the `proxmox` boot entry is pointing to a Grub installation
-on a disk, where the disk itself not a boot option. If possible, try adding the
-disk as a boot option in the UEFI firmware setup utility and run
+on a disk, where the disk itself is not a boot option. If possible, try adding
+the disk as a boot option in the UEFI firmware setup utility and run
 `proxmox-boot-tool` again.
 
 TIP: To enroll custom keys, see the accompanying