move swapfile expansion steps to pre-requisites (team#41187)

it's assumed that /swapfile exists in /etc/fstab, all installers should
be setting it up

howto/new-machine.md

@@ -70,6 +70,17 @@ taken by the installer:
  0. partitions have been correctly setup, including some (>=512M) swap
     file (or swap partition) and a `tmpfs` in `/tmp`
 
+    consider expanding the swap file if memory requirements are
+    expected to be higher than usual on this system, such a large database
+    servers, GitLab instances, etc. the steps below will recreate a 1G
+    `/swapfile` volume:
+
+        swapoff -a &&
+        dd if=/dev/zero of=/swapfile bs=1M count=1024 &&
+        chmod 0600 /swapfile &&
+        mkswap /swapfile &&
+        swapon -a
+
  1. a minimal Debian install with security updates has been booted
     (note that Puppet will deploy unattended-upgrades later, but it's
     still a good idea to do those updates as soon as possible)
@@ -254,18 +265,7 @@ above](#pre-requisites)! Some installers cover all of those steps, but most do n
         printf 'UUID=%s\t/srv\text4\tdefaults\t1\t2\n' $(blkid --match-tag UUID --output value /dev/sdc) >> /etc/fstab  &&
         mount /srv
 
- 9. consider expanding the swap file if memory requirements are
-    expected to be higher than usual on this system, such a large database
-    servers, GitLab instances, etc. the steps below will recreate a 1G
-    `/swapfile` volume:
-
-        swapoff -a &&
-        dd if=/dev/zero of=/swapfile bs=1M count=1024 &&
-        chmod 0600 /swapfile &&
-        mkswap /swapfile &&
-        swapon -a
-
- 10. once everything is done, reboot the new machine to make sure
+ 9. once everything is done, reboot the new machine to make sure
     *that* still works:
 
         reboot