[docs] add reference to ASF software release policy
[docs] add reference to ASF software release policy

Change-Id: Ic8e5525b2d6c7046e69715d6e9d99d588c80f246
Reviewed-on: http://gerrit.cloudera.org:8080/14561
Tested-by: Kudu Jenkins
Reviewed-by: Andrew Wong <b68e4fdc6430321a6b47400732ff97d7ae91234e@cloudera.com>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu