man: use title of docs/ pages when referring to them

There is some inconsistency, partially caused by the awkward naming
of the docs/ pages. But let's be consistent and use the "official" title.
If we ever change plural↔singular, we should use the same form everywhere.

man/nss-systemd.xml

@@ -67,7 +67,7 @@
 
     <para>This is a simple mechanism to provide static user and group records via JSON drop-in files. Such
     user records should be defined in the format described by the <ulink
-    url="https://systemd.io/USER_RECORD">JSON User Record</ulink> specification and be placed in one of the
+    url="https://systemd.io/USER_RECORD">JSON User Records</ulink> specification and be placed in one of the
     aforementioned directories under a file name composed of the user name suffixed with
     <filename>.user</filename>, with a world-readable access mode. A symlink named after the user record's
     UID formatted in decimal and suffixed with <filename>.user</filename> pointing to the primary record file

man/pam_systemd.xml

@@ -33,7 +33,7 @@
     and hence the systemd control group hierarchy.</para>
 
     <para>The module also applies various resource management and runtime parameters to the new session, as
-    configured in the <ulink url="https://systemd.io/USER_RECORD">JSON User Record</ulink> of the user, when
+    configured in the <ulink url="https://systemd.io/USER_RECORD">JSON User Records</ulink> of the user, when
     one is defined.</para>
 
     <para>On login, this module — in conjunction with <filename>systemd-logind.service</filename> — ensures the

man/systemd-portabled.service.xml

@@ -35,8 +35,8 @@
     <para>Most of <command>systemd-portabled</command>'s functionality is accessible through the
     <citerefentry><refentrytitle>portablectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> command.</para>
 
-    <para>See the <ulink url="https://systemd.io/PORTABLE_SERVICES">Portable
+    <para>See <ulink url="https://systemd.io/PORTABLE_SERVICES">Portable Services</ulink> for details about
-    Services Documentation</ulink> for details about the concepts this service implements.</para>
+    the concepts this service implements.</para>
   </refsect1>
 
   <refsect1>

man/systemd-sysext.xml

@@ -71,7 +71,7 @@
     <orderedlist>
       <listitem><para>Plain directories or btrfs subvolumes containing the OS tree</para></listitem>
       <listitem><para>Disk images with a GPT disk label, following the <ulink
-      url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partition Specification</ulink></para></listitem>
+      url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partitions Specification</ulink></para></listitem>
       <listitem><para>Disk images lacking a partition table, with a naked Linux file system (e.g. squashfs or ext4)</para></listitem>
     </orderedlist>
 

man/systemd-userdbd.service.xml

@@ -41,7 +41,7 @@
     command.</para>
 
     <para>The user and group records this service provides access to follow the <ulink
-    url="https://systemd.io/USER_RECORD">JSON User Record</ulink> and <ulink
+    url="https://systemd.io/USER_RECORD">JSON User Records</ulink> and <ulink
     url="https://systemd.io/GROUP_RECORD">JSON Group Record</ulink> definitions. This service implements the
     <ulink url="https://systemd.io/USER_GROUP_API">User/Group Record Lookup API via Varlink</ulink>, and
     multiplexes access other services implementing this API, too. It is thus both server and client of this

man/systemd.exec.xml

@@ -241,7 +241,7 @@
         <para>This option is supported only for disk images that contain a single file system, without an
         enveloping partition table. Images that contain a GPT partition table should instead include both
         root file system and matching Verity data in the same image, implementing the <ulink
-        url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partition Specification</ulink>.</para>
+        url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partitions Specification</ulink>.</para>
 
         <xi:include href="system-only.xml" xpointer="singular"/></listitem>
       </varlistentry>