Added more details about the use of configuration fragments in Skylark to the documentation.
Added more details about the use of configuration fragments in Skylark to the documentation.

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MOS_MIGRATED_REVID=101357875

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