HPCC-7879 Interface example not self contained, add comment

Signed-off-by: Richard Taylor <richard.taylor@lexisnexis.com>
Merge pull request #4311 from RichardTaylorHPCC/B7879

HPCC-7879 Interface example not self contained, add comment

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>