update REDME

README.md

@@ -12,7 +12,9 @@ Options:
 * `outbound-relays.techservices.illinois.edu`
   * Recommended for hosts in NCSA Public IP space (141.142.0.0/16)
     * Note: must also have a public hostname (e.g. *.illinois.edu) and
-      that hostname must be set in `myhostname` and `myorigin`
+      that hostname must be set in `myhostname` and `myorigin`. This works fine
+      for the most common case when a node has just one hostname and one IP,
+      but more care is needed when a node has multiple names or IPs.
 
 See also:
 * [University of Illinois IP Spaces](https://go.illinois.edu/ipspace)