Documentation : Advise against a high TTL during Geo setup, to improve DR and Planned Failover

The following discussion from !5284 (merged) should be addressed:

• @brodock started a discussion: (+1 comment)

  Does it make sense for us to provide a section in the documentation explaining how to prepare your setup for disaster recovery promotion? Where we explain the tradeoffs of changing the primary DNS vs keeping URLs intact and that you may want to keep a relatively lower TTL always, in order to support this type of change?

  What my goal is here is that, if you have a very high TTL (like 86400, changing it to 5 minutes, 60 seconds etc when a disaster happens, will be too late)