KUDU-1530: Update docs about OS X build dependency on Xcode package
KUDU-1530: Update docs about OS X build dependency on Xcode package

Change-Id: I8962d5539f437dba8b120c70c90c1e384ed550c9
Reviewed-on: http://gerrit.cloudera.org:8080/3653
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: Mike Percy <e07a1fd797b473a9c849e618aa2ce06d8055760b@apache.org>
Reviewed-by: Mike Percy <e07a1fd797b473a9c849e618aa2ce06d8055760b@apache.org>

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