Add build status image to readme.md file.
completed by: Piotr
mentors: Aruna Herath
Add the travis build status image that shows the build health of fossasia.github.io to the project's README.md file.
Useful links
Travis status images: http://docs.travis-ci.com/user/status-images/
Github repo: https://github.com/fossasia/fossasia.github.io
Travis CI: https://travis-ci.org/fossasia/fossasia.github.io