Initial usage added to README
Initial usage added to README

Currently any usage information is missing and thus starting with some initial details.
bazelbuild/bazel-buildfarm,bazelbuild/bazel-buildfarm,bazelbuild/bazel-buildfarm,bazelbuild/bazel-buildfarm,bazelbuild/bazel-buildfarm,bazelbuild/bazel-buildfarm,bazelbuild/bazel-buildfarm