Update README for AS 2.4 Preview 4
Update README for AS 2.4 Preview 4

Reviewers: O2 Material Motion, #material_motion, featherless

Reviewed By: O2 Material Motion, #material_motion, featherless

Tags: #material_motion

Differential Revision: http://codereview.cc/D3057

material-motion/material-motion-android,material-motion/material-motion-android