Update "repmgr node rejoin" documentation

doc/repmgr-node-rejoin.sgml

@@ -6,8 +6,41 @@
   <para>
    Enables a dormant (stopped) node to be rejoined to the replication cluster.
   </para>
+  <note>
+   <simpara>
+     Currently <command>repmgr node rejoin</command> can only be used to attach
+     a standby to the current primary, not another standby.
+   </simpara>
+  </note>
   <para>
     This can optionally use <command>pg_rewind</command> to re-integrate a node which has diverged
     from the rest of the cluster, typically a failed primary.
   </para>
+  <para>
+    The node must have been shut down cleanly; if this was not the case, it will
+    need to be manually started (remove any existing <filename>recovery.conf</filename> file) until
+    it has reached a consistent recovery point, then shut down cleanly.
+  </para>
+  <para>
+    Usage:
+    <programlisting>
+      repmgr node rejoin -d '$conninfo'</programlisting>
+
+    where <literal>$conninfo</literal> is the conninfo string of any reachable node in the cluster.
+    <filename>repmgr.conf</filename> for the stopped node *must* be supplied explicitly if not
+    otherwise available.
+  </para>
+  <para>
+    <command>repmgr node rejoin</command> can optionally use <command>pg_rewind</command> to re-integrate a
+    node which has diverged from the rest of the cluster, typically a failed primary.
+    <command>pg_rewind</command> is available in PostgreSQL 9.5 and later.
+  </para>
+  <note>
+    <para>
+      <command>pg_rewind</command> *requires* that either <varname>wal_log_hints</varname> is enabled, or that
+      data checksums were enabled when the cluster was initialized. See the
+      <ulink url="https://www.postgresql.org/docs/current/static/app-pgrewind.html"><command>pg_rewind</command> documentation</ulink> for details.
+
+    </para>
+  </note>
 </chapter>