Add Gitbook build support

[sabertazimi]

With Gitbook and Travis CI, building an online version of this tutorial only need 2 steps

Gitbook Live Demo -> Repo

Enable CI build on travis.org

Just need to complete step 2 of https://docs.travis-ci.com/user/getting-started#To-get-started-with-Travis-CI

Define GITHUB_TOKEN, GIT_NAME and GIT_EMAIL environment variables

As https://docs.travis-ci.com/user/environment-variables/#Defining-Variables-in-Repository-Settings said, set:

• GITHUB_TOKEN with repo access to deploy building result to gh-pages branch
• GIT_NAME to cyan33
• GIT_EMAIL to cyan.binary@gmail.com

[cyan33]

That looks awesome. Thanks @sabertazimi 👍

[cyan33]

Would you also like to add this link to the README file?

[sabertazimi]

OK