Add references to other tools for ‘zerotier-one’.

doc/zerotier-one.8.txt

@@ -83,6 +83,8 @@ specified `HOMEDIR` directory (default: ``/var/lib/zerotier-one``).
 SEE ALSO
 ========
 
+* **zerotier-idtool**\ (1), **zerotier-cli**\ (1)
+
 * ZeroTier One documentation:
 
   * Product page `<https://www.zerotier.com/product-one.shtml>`__.