[doc] note on having at least 3 locations for better HA

This patch adds a note on defining at least three locations to increase
the availability of a Kudu cluster when location awareness is enabled.
Sure, it's obvious if understanding how the placement policy works,
but for the first-time readers it might be a good heads-up.

Change-Id: Ib0d8d2e7d917205c62aca567eb2b2db540f7857e
Reviewed-on: http://gerrit.cloudera.org:8080/16514
Tested-by: Kudu Jenkins
Reviewed-by: Greg Solovyev <gsolovyev@cloudera.com>
Reviewed-by: Andrew Wong <awong@cloudera.com>
1 file changed