[Issue #229] In 'remote operations' section add requirement about programm version

Author: gsmolk

doc/pgprobackup.xml

@@ -1081,6 +1081,13 @@ GRANT SELECT ON TABLE pg_catalog.pg_database TO backup;
             <xref linkend="pbk-archive-get"/>.
           </para>
         </listitem>
+        <listitem>
+          <para>
+            Operating in remote mode requires <application>pg_probackup</application>
+            binary to be installed on both local and remote systems.
+            The versions of local and remote binary must be the same.
+          </para>
+        </listitem>
         <listitem>
           <para>
             When started in the remote mode, the main <application>pg_probackup</application> process