[3429] Minor fixes to the text added by Jeremy.

doc/guide/dhcp4-srv.xml

@@ -248,7 +248,7 @@ url="http://jsonviewer.stack.hu/"/>.
   Memfile backend will write leases to a disk in the
   [kea-install-dir]/var/kea/kea-leases4.csv. -->
   The following configuration sets the name of the lease file to
-  /tmp/kea-leases4.csv:
+  <filename>/tmp/kea-leases4.csv</filename>:
 
 <screen>
 "Dhcp4": {

doc/guide/dhcp6-srv.xml

@@ -255,7 +255,7 @@ JSON validator is available at <ulink url="http://jsonviewer.stack.hu/"/>.
   Memfile backend will write leases to a disk in the
   [kea-install-dir]/var/kea/kea-leases4.csv. -->
   The following configuration sets the name of the lease file to
-  /tmp/kea-leases6.csv:
+  <filename>/tmp/kea-leases6.csv</filename>:
 
 <screen>
 "Dhcp6": {

doc/guide/intro.xml

@@ -142,7 +142,7 @@
             <simpara>
               <command>perfdhcp</command> &mdash;
               DHCP benchmarking tool which simulates multiple clients to
-              test both IPv4 and IPv6 servers performance.
+              test both DHCPv4 and DHCPv6 servers performance.
             </simpara>
           </listitem>