Fix links on doc pages that were pointing to .md files.
Fix links on doc pages that were pointing to .md files.

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MOS_MIGRATED_REVID=131832236

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