Documentation: fix docs of value of --show_progress_rate_limit.
Documentation: fix docs of value of --show_progress_rate_limit.

Default value was wrong and semantics were not documented in enough detail.

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MOS_MIGRATED_REVID=96312299

bazelbuild/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,bazelbuild/bazel-website