Elaborate a bit on Impala's prerequisites
Elaborate a bit on Impala's prerequisites

Change-Id: Idceb7232c802a861192bd555778f6336a4d5a409
Reviewed-on: http://gerrit.cloudera.org:8080/1187
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>
Tested-by: Misty Stanley-Jones <b9f9ef9e00c258208ea831c64cc129eda4ac78b4@apache.org>

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