Add DIR_METADATA to //codelabs

Bug: N/A
Change-Id: I2fa776ab02969c19fec3cc1bffd0745a181da598
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488393Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Austin Sullivan <asully@chromium.org>
Auto-Submit: Austin Sullivan <asully@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820458}

codelabs/DIR_METADATA

+# Metadata information for this directory.
+#
+# For more information on DIR_METADATA files, see:
+#   https://source.chromium.org/chromium/infra/infra/+/master:go/src/infra/tools/dirmd/README.md
+#
+# For the schema of this file, see Metadata message:
+#   https://source.chromium.org/chromium/infra/infra/+/master:go/src/infra/tools/dirmd/proto/dir_metadata.proto
+
+monorail {
+  component: "Infra>Documentation"
+}
+team_email: "infra-dev@chromium.org"
\ No newline at end of file