Updating the docs with a new tested NDK version.
Updating the docs with a new tested NDK version.

The docs now reflect a tested version of the NDK, to help
prevent any confusion from errors that occur with older NDK
versions.

Bug: b/25397549
Change-Id: I38f6270637f7e864600d0a1e4607991bc36b062d
Tested: Tested on mac with generate_docs.py and viewed on Chrome.

google/flatui,google/flatui,google/flatui,google/flatui