Documentation issue: Installing Bazel using Bazelisk

Documentation URL: https://docs.bazel.build/versions/master/install-bazelisk.html

This page suggests using `go get` to install Bazelisk in some cases, but that doesn't actually produce a `bazel` binary that users can invoke.

This is closely related to the Bazelisk issue: https://github.com/bazelbuild/bazelisk/issues/162
I'm filing *this* issue mostly to make sure that Bazel's documentation gets updated to match.

But maybe the Bazel docs could be updated more rapidly in the interim to make it clear what users are supposed to do in addition to `go get` to install Bazelisk on platforms without Homebrew or NPM.

FWIW, I also don't really understand how to follow the instructions to "use the binary release" -- the releases aren't in any standard package format and so it isn't clear what exactly is the correct process to install and use those binary releases.

Start with the installation page at docs.bazel.build/versions/master/install-bazelisk.html and compare its `go get` and binary-release instructions with Bazelisk issue #162. Clarify the steps needed to obtain an invokable `bazel` binary on platforms without Homebrew or NPM. Done means the page accurately explains both installation paths and how to use binary releases.

Written by the indexing model from the issue text.