UsingTravis: add Deploying GitHub Pages section

docs/UsingTravis.adoc

@@ -54,6 +54,48 @@ image:travis_build.png[Travis build]
 .  If the build is successful, you should be able to check the coverage details of the tests at http://coveralls.io/[Coveralls]
 .  Update the link to the 'build status' badge at the top of the `README.adoc` to point to the build status of your own repo.
 
+== Deploying GitHub Pages
+
+.  Ensure that you have followed the steps above to set up Travis CI.
+.  On GitHub, create a new user account and give this account collaborator and admin access to the repo. +
+   Using this account, generate a personal access token https://github.com/settings/tokens/new[here].
++
+[NOTE]
+Personal access tokens are like passwords so make sure you keep them secret! If the personal access token is leaked, please delete it and generate a new one.
++
+[NOTE]
+We use a new user account to generate the token for team projects to prevent team members from gaining access to other team members' repos. +
+If you are the only one with write access to the repo, you can use your own account to generate the token.
++
+--
+* Add a description for the token. (e.g. `Travis CI - deploy docs to gh-pages`)
+* Check the `public_repo` checkbox.
+* Click `Generate Token` and copy your new personal access token.
+--
+We will use this token to grant Travis access to the repo.
++
+image:generate_token.png[Generate token]
+
+.  Head to the https://travis-ci.org/profile[Accounts] page, and find the switch for the forked repository.
++
+image:flick_repository_switch.png[Activate the switch]
++
+.  Click on the settings button next to the switch. In the Environment Variables section, add a new environment variable with
++
+--
+* name: `GITHUB_TOKEN`
+* value: personal access token copied in step 1
+* Display value in build log: `OFF`
+--
+image:travis_add_token.png[Travis add token]
++
+[NOTE]
+*Make sure you set `Display value in build log` to `OFF`.* +
+Otherwise, other people will be able to see the personal access token and thus have access this repo. +
+Similarly, make sure you *do not print `$GITHUB_TOKEN` to the logs* in Travis scripts as the logs are viewable by the public.
+
+.  Now, whenever there's a new commit to master branch, Travis will push the latest documentation to gh-pages branch.
+
 == Repository-wide checks
 
 In addition to running Gradle checks, we also configure Travis CI to run some repository-wide checks. Unlike the Gradle checks which only cover files used in the build process, these repository-wide checks cover _all_ files in the repository. They check for repository rules which are hard to enforce on development machines such as line ending requirements.