Merge pull request #119 from soulmachine/master

A little revise for the document

(cherry picked from commit f0e23a023ce1356bc0f04248605c48d4d08c2d05)
Signed-off-by: Reynold Xin <rxin@apache.org>
Merge branch 'branch-0.8' of https://github.com/apache/incubator-spark into master-csd