Document or Ignore Configuration Collisions

[jcaprice]

Web Manager will throw an error if any of session-ttl-seconds, config-location, or client-config-location are configured in conjunction with instance-name. This specific behavior is undocumented in the README. The README also says session-ttl-seconds will be ignored in client/server mode.

I've submitted this as an issue, rather than as a PR changing the README, to see if these settings should be ignored if instance-name is configured or if we should update the README to indicate Web Manager will not start with these settings configured together.