Document how to generate the html documentation
Document how to generate the html documentation

It is a bit meta, I needed a way to generate the flat html files (not
the searchfree bundle). Turns out it is just about running:

  bazel build Documentation:Documentation

And opening `bazel-bin/Documentation/index.html`.

Since not everyone is familiar with bazel targets or how to discover the
`Documentation:Documentation` target, document it.

Change-Id: Icc27f8c2433ef232ba8951dbe058589ef4cf1d66

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