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Closes #951 from pan3793/license.

Closes #951

4629eecd [Cheng Pan] Fix
c45a0784 [Cheng Pan] nit
b9a46b42 [Cheng Pan] pin license header at first line
80d1a71b [Cheng Pan] nit
b2a46e4c [Cheng Pan] Update
f6acaaf8 [Cheng Pan] minor
ef99183f [Cheng Pan] Add license header on all docs
Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: Cheng Pan <chengpan@apache.org>
(cherry picked from commit a76c3440

)
Signed-off-by: Cheng Pan <chengpan@apache.org>