IMPALA-3808: Add incubating DISCLAIMER from the Incubator Branding Guide
IMPALA-3808: Add incubating DISCLAIMER from the Incubator Branding Guide

See http://incubator.apache.org/guides/branding.html

Change-Id: Ifac8245d2dd68fd7f9524fb1a1564ba730394b37
Reviewed-on: http://gerrit.cloudera.org:8080/4160
Reviewed-by: Jim Apple <9e3620e7251463d214b5f536438d2c9ea899162d@cloudera.com>
Tested-by: Internal Jenkins

michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala