quality: Update README

.travis.yml

@@ -1,6 +1,13 @@
 language: elixir
+
 elixir:
   - 1.8.1
+
 otp_release:
   - 21.0
-script: mix test
+
+script:
+  - MIX_ENV=test mix do compile --warnings-as-errors, coveralls.json
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)

README.md

@@ -1,5 +1,7 @@
 # Tres - an Elixir OpenFlow development platform
 
+[![Build Status](https://travis-ci.org/shun159/tres.svg?branch=develop)](https://travis-ci.org/shun159/tres)
+
 ## Overview
 
 Tres is a framework and set of helper libraries to develop OpenFlow controllers in Elixir.