Add documentation for Bazel 

We recently merged Bazel support in #439 but this functionality is currently undocumented. For now, we have an end-to-end example in the repo that Bazel users can look at https://github.com/sourcegraph/lsif-java/blob/e0fbe110dfa085cbe1053a6584d79e7bf985997f/examples/bazel-example/WORKSPACE

This issue is about adding documentation to the lsif-java website.