[LIB] add Travis' badge on the README
[LIB] add Travis' badge on the README

Summary:
This Differential has no code changes, it only add a Travis build badge to the README.

fixes T7

Test Plan: No changes. Verify the README on [Github](https://github.com/go-acd/acd).

Reviewers: #go_amazon_cloud_drive, kalbasit

Reviewed By: #go_amazon_cloud_drive, kalbasit

Maniphest Tasks: T7

Differential Revision: http://phabricator.nasreddine.com/D2

go-acd/acd,InboundAzimuth/acd