Update index.md to explain 1.6 configuration, now that 1.6 has been released.
Update index.md to explain 1.6 configuration, now that 1.6 has been released.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190546700

eamonnmcmanus/auto,eamonnmcmanus/auto,google/auto,google/auto,google/auto,eamonnmcmanus/auto