man: document --prompt-new-user which was added back in v256

(cherry picked from commit 6f496236bc)

man/homectl.xml

@@ -205,6 +205,16 @@
         <xi:include href="version-info.xml" xpointer="v258"/></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>--prompt-new-user</option></term>
+
+        <listitem><para>If used in conjunction with <command>firstboot</command> and no regular user account
+        exists on the system so far the tool will interactively query for user information and create an
+        account.</para>
+
+        <xi:include href="version-info.xml" xpointer="v256"/></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>--match=</option></term>
         <term><option>-A</option></term>
@@ -1424,9 +1434,10 @@ $ ssh lennart@targetsystem</programlisting>
 
         <listitem><para>This command is supposed to be invoked during the initial boot of the system. It
         checks whether any regular home area exists so far, and if not queries the user interactively on the
-        console for user name and password and creates one. Alternatively, if one or more service credentials
-        whose name starts with <literal>home.create.</literal> are passed to the command (containing a user
-        record in JSON format) these users are automatically created at boot.</para>
+        console for user name and password and creates one (only if <option>--prompt-new-user</option> is
+        specified). Alternatively, if one or more service credentials whose name starts with
+        <literal>home.create.</literal> are passed to the command (containing a user record in JSON format)
+        these users are automatically created at boot.</para>
 
         <para>This command is invoked by the <filename>systemd-homed-firstboot.service</filename> service
         unit.</para>