man: encourage the creation of empty machine-id instead of deleting it

Current text hints that machine-id in template image should be empty
if the system is read-only. But most of the bare metal systems and
regular VMs have /etc read-only at this phase of boot.

(cherry picked from commit 64fcb07)
(cherry picked from commit 5f55879673b119ebc98280518a9ab5bb7f4b1c5d)
(cherry picked from commit 8ee0c2ee0ca8be0a34e9528b11e912735e8b5a33)
(cherry picked from commit 6e9eba2)
(cherry picked from commit df71727)

Author: lnykryn

man/machine-id.xml

@@ -84,9 +84,9 @@
     containers or in the cloud, <filename>/etc/machine-id</filename> should be either missing or an empty
     file in the generic file system image (the difference between the two options is described under "First
     Boot Semantics" below). An ID will be generated during boot and saved to this file if possible. Having an
-    empty file in place is useful because it allows a temporary file to be bind-mounted over the real file,
-    in case the image is used read-only. Also see <ulink url="https://systemd.io/BUILDING_IMAGES">Safely
-    Building Images</ulink>.</para>
+    empty file in place is recommended because it allows a temporary file to be bind-mounted over the real file,
+    in case the image is used read-only and when <filename>/etc</filename> is mounted read-only in the early boot.
+    Also see <ulink url="https://systemd.io/BUILDING_IMAGES">Safely Building Images</ulink>.</para>
 
     <para><citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
     may be used to initialize <filename>/etc/machine-id</filename> on mounted (but not