Add .travis.yml and add the build status badge to the README.
Example build on my fork: https://travis-ci.org/rfjakob/cryptoWallet/builds/394753550
You will need to enable Travis on your repository on
https://travis-ci.org/profile/xaionaro-go so that automatic builds
and the status badge works.
The Go versions that are built are the same that gocryptfs uses
in its travis config.