Clarify supported ranks for new ops in R

Fix: 151108533
Test: mma
Change-Id: I85b66ab5940d09b2786ecb14bff5bc1c1dee894a
Merged-In: I85b66ab5940d09b2786ecb14bff5bc1c1dee894a
(cherry picked from commit f161cc74a11b7468f5adc51cdfbbc3d5dd87f51a)
2 files changed