readme: Apply small updates to install commands

They don’t change much (if at all), but it makes the installation guide
more streamlined.

README.md

@@ -66,7 +66,7 @@ On MBR:
 Format encrypted partition and open it:
 
     cryptsetup luksFormat --type luks2 /dev/nvmeXnYp2
-    cryptsetup open --type luks2 /dev/nvmeXnYp2 HOSTNAME-pv
+    cryptsetup open /dev/nvmeXnYp2 HOSTNAME-pv
 
 Create LVM (replace `8G` with desired swap size):
 
@@ -93,7 +93,7 @@ On MBR:
 
 Mount the file systems and activate swap:
 
-    mount /dev/HOSTNAME-vg/root /mnt
+    mount -o compress=zstd /dev/HOSTNAME-vg/root /mnt
     mkdir /mnt/boot
     mount /dev/nvmeXnYp1 /mnt/boot
     swapon /dev/HOSTNAME-vg/swap