Add Travis / Go & OpenFaaS GitHub badges to README.md

[alexellis]

Expected Behaviour

We should have Travis / Go & OpenFaaS GitHub badges in our README.md file just like openfaas/faas openfaas/faas-netes openfaas/faas-cli and etc.

Current Behaviour

Not shown, manually have to discover the build if it's passing/failing or a PR etc.

Possible Solution

See the repos mentioned above and retrofit for this project.