Write a tutorial, linked from Bazel front page

https://bazel.build/ has tutorials for Java, C++, iOS, and Android, linked from the bottom of the home page. Each tutorial has language-specific setup instructions, but also covers general Bazel concepts (WORKSPACE, BUILD files, rules, etc).

We should have a tutorial for Go. This is especially important since we have some Go-specific steps (WORKSPACE boilerplate, running Gazelle, etc).

It probably doesn't make sense to write this today, since the API and Gazelle are changing quickly, but this should be written soon, certainly by the end of 2017Q3.

Start by reviewing the existing Java, C++, iOS, and Android tutorials linked from bazel.build, then compare their general Bazel coverage with the Go-specific WORKSPACE and Gazelle steps described here. Done means a Go tutorial covering those concepts and setup steps is published and linked from the Bazel front page.

Written by the indexing model from the issue text.