Add release-notes for Vumi 0.3.1.
Add release-notes for Vumi 0.3.1.

TouK/vumi,vishwaprakashmishra/xmatrix,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi,harrissoerja/vumi