Add an example of using a regex with negative lookup in --output_filter.
Add an example of using a regex with negative lookup in --output_filter.

I promised to add this example after responding to a user question in the bazel irc.

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MOS_MIGRATED_REVID=102120516

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