Add information to the --help and docs of standby clone regarding the need

to provide a conninfo line to the upstream from which we will be cloning
from.

doc/repmgr-standby-clone.sgml

@@ -213,6 +213,15 @@
 
     <variablelist>
 
+      <varlistentry>
+        <term><option>-d, --dbname=CONNINFO</option></term>
+        <listitem>
+          <para>
+            Connection string of the upstream node to use for cloning.
+          </para>
+        </listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>--dry-run</option></term>
         <listitem>

repmgr-action-standby.c

@@ -6513,6 +6513,7 @@ do_standby_help(void)
 	puts("");
 	printf(_("  \"standby clone\" clones a standby from the primary or an upstream node.\n"));
 	puts("");
+	printf(_("  -d, --dbname=conninfo               conninfo of the upstream node to use for cloning.\n"));
 	printf(_("  -c, --fast-checkpoint               force fast checkpoint\n"));
 	printf(_("  --copy-external-config-files[={samepath|pgdata}]\n" \
 			 "                                      copy configuration files located outside the \n" \